Head to savemyexams.co.uk for more awesome resources AS Chemistry CIE 3. Organic Chemistry CONTENTS 3.1 An Introduction to AS Level Organic Chemistry 3.1.1 Hydrocarbons & Alkanes 3.1.2 Functional Groups and their Formulae 3.1.3 Naming of Organic Compounds 3.1.4 Molecular & Empirical Formulae 3.1.5 Characteristic Organic Reactions 3.1.6 Terminology Used in Reaction Mechanisms 3.1.7 Shapes of Organic Molecules; Sigma & Pi Bonds 3.1.8 Hybridisation in Organic Molecules 3.1.9 Planarity of Organic Molecules 3.1.10 Structural Isomerism 3.1.11 Stereoisomerism 3.1.12 Chirality 3.1.13 Isomers of Organic Compounds 3.2 Hydrocarbons 3.2.1 Alkanes 3.2.2 Combustion & Free Radical Substitution of Alkanes 3.2.3 Free Radical Substitution 3.2.4 Cracking of Alkanes 3.2.5 Chemical Reactivity of Alkanes 3.2.6 Combustion of Alkanes 3.2.7 Production of Alkenes 3.2.8 Reactions of Alkenes 3.2.9 Test for Unsaturation 3.2.10 Electrophilic Addition of Alkenes 3.2.11 Markovnikov's Rule 3.3 Halogen Compounds 3.3.1 Production of Halogenoalkanes 3.3.2 Substitution Reactions of Halogenoalkanes 3.3.3 Elimination Reactions of Halogenoalkanes 3.3.4 SN1 & SN2 3.3.5 Reactivity of Halogenoalkanes Page 1 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.4 Hydroxy Compounds 3.4.1 Production of Alcohols 3.4.2 Reactions of Alcohols 3.4.3 Classifying and Testing for Alcohols 3.4.4 Alcohol Dissociation 3.5 Carbonyl Compounds 3.5.1 Production of Aldehydes & Ketones 3.5.2 Reactions of Aldehydes & Ketones 3.5.3 Reaction with HCN 3.5.4 Carbonyl Compound Tests 3.5.5 Iodoform Reaction 3.6 Carboxylic Acids & Derivatives 3.6.1 Carboxylic Acids 3.6.2 Esters 3.7 Nitrogen Compounds 3.7.1 Primary Amines 3.7.2 Nitriles & Hydroxynitriles 3.8 Polymerisation 3.8.1 Addition Polymerisation 3.8.2 Disposal of Polymers 3.9 Organic Synthesis 3.9.1 Organic Synthesis 3.9.2 Multi-Step Synthesis 3.9.3 Synthetic Routes Page 2 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources 3.1 An Introduction to AS Level Organic Chemistry 3.1.1 Hydrocarbons & Alkanes Homologous Series Organic chemistry is the chemistry of carbon compounds Carbon forms a vast number of compounds because it can form strong covalent bonds with itself This enables it to form long chains of carbon atoms, branched chains or cycles, and hence an almost infinite variety of carbon compounds are known Carbon always forms four covalent bonds which can be single, double or triple bonds There is an almost infinite variety of chains, branches and rings able to form A functional group is a specific atom or group of atoms which confer certain physical and chemical properties onto the molecule Organic molecules are classified by the dominant functional group on the molecule Organic compounds with the same functional group, but with each successive member different by CH2 are called a homologous series Every time a carbon atom is added to the chain, two hydrogen atoms are also added, which is why the successive members differ by CH2 Page 3 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Hydrocarbons YOUR NOTES Hydrocarbons are compounds that are made up of carbon and hydrogen atoms ONLY The diagram shows examples of hydrocarbons Ethanol is NOT a hydrocarbon as the molecule also contains an oxygen atom and is not solely made up of carbon and hydrogen Tip Exam You must state that hydrocarbons are ‘only’ made up of C and H atoms if defining this term in an exam Page 4 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Alkanes YOUR NOTES A functional group is an atom or a group of atoms in an organic molecule, which determines the physical and chemical properties of the molecule Alkanes are the simplest hydrocarbons with no functional group They are made up of carbon and hydrogen atoms bonded to each other with single covalent bonds Alkanes are compounds made up of carbon and hydrogen atoms only and contain no functional group Homologous Series of Alkanes Table Page 5 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.2 Functional Groups and their Formulae Functional Groups of Organic Compounds Functional groups determine the physical and chemical properties of molecules The table below shows a summary of common functional groups found in compounds R is any other atom or group of atoms (except for hydrogen) Functional groups found in compounds table Page 6 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Formulae of Organic Compounds The general formula is a formula that represents a homologous series of compounds using letters and numbers Eg. the general formula of alkanes is CnH2n+2 A homologous series is a group of organic compounds that have the same functional group, the same general formula and the same chemical properties The structural formula is a formula that shows how the atoms are bonded to each carbon atom in a molecule The displayed formula is a 2D representation of an organic molecule showing all its atoms (by their symbols) and their bonds (by single, double or triple bonds) The skeletal formula is a simplified displayed formula with all the carbon and hydrogen (CH) bonds removed Overview of the formulae of organic compounds table Worked example: Drawing skeletal formulae of molecules Page 7 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Worked example: Drawing displayed formulae of molecules Page 8 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 9 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.3 Naming of Organic Compounds Nomenclature of Aliphatic Compounds Systematic nomenclature can be used to name organic compounds and therefore make it easier to refer to them The alkanes provide the basis of the naming system and the stem of each name indicates how many carbon atoms are in the longest chain in one molecule of the compound Nomenclature of organic compounds table If there are any side-chains or functional groups present, then the position of these groups are indicated by numbering the carbon atoms in the longest chain starting at the end that gives the lowest possible numbers in the name The hydrocarbon side-chain is shown in brackets in the structural formula CH3CH(CH3)CH2CH3 Page 10 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources The side-chain is named by adding ‘-yl’ to the normal alkane stem This type of group is called an alkyl group If there are more than one of the same alkyl side-chain or functional groups, di- (for two), tri- (for three) or tetra- (for four) is added in front of its name The adjacent numbers have a comma between them Numbers are separated from words by a hyphen If there is more than one type of alkyl side-chain, they are listed in alphabetic order Page 11 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Functional groups & their nomenclature table Page 12 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Worked example: Naming organic molecules Page 13 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Tip Exam An aliphatic compound is straight or branched-chain and also includes cyclic organic compounds that do not contain a benzene ring. Page 14 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.4 Molecular & Empirical Formulae Molecular & Empirical Formulae of Organic Compounds The molecular formula shows the number and type of each atom in a molecule Eg. the molecular formula of ethanoic acid is C2H4O2 The empirical formula shows the simplest whole number ratio of the elements present in one molecule of the compound Eg. the empirical formula of ethanol is CH2O Worked example: Deducing molecular & empirical formulae Page 15 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 16 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.5 Characteristic Organic Reactions Definitions & Terminology in Organic Chemistry Homologous series A homologous series is a group of organic compounds that have the same functional group, the same general formula and the same chemical properties Ethanol and propanol belong to the same homologous series Saturated & unsaturated hydrocarbons Saturated hydrocarbons are hydrocarbons which contain single bonds only resulting in the maximum number of hydrogen atoms in the molecule Unsaturated hydrocarbons are hydrocarbons which contain carbon-carbon double or triple bonds Page 17 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The diagram shows saturated hydrocarbons which contain single bonds only and unsaturated hydrocarbons which contain double/triple bonds as well Homolytic & heterolytic fission Homolytic fission is breaking a covalent bond in such a way that each atom takes an electron from the bond to form two radicals Heterolytic fission is breaking a covalent bond in such a way that the more electronegative atom takes both the electrons from the bond to form a negative ion and leaving behind a positive ion Page 18 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The diagram shows heterolytic fission in which the most electronegative atom takes both electrons in the covalent bond and homolytic fission in which each atom takes one electron from the covalent bond Radical chain reactions A free radical is a species with one (or more than one) unpaired electrons The diagram shows a free radical which has one unpaired electron A free radical reaction is a reaction involving free radicals and is a three-step reaction: Initiation is the first step and involves breaking a covalent bond using energy from ultraviolet (UV) light from the sun to form two free radicals Page 19 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources The propagation step is the second step in which the formed radical can attack reactant molecules to form even more radicals These in turn can again attack other molecules to form more free radical and so on In the termination step, two free radicals react together to form a product molecule The diagram shows the different stages of a radical chain reactions Nucleophiles & electrophiles A nucleophile is an electron-rich species that can donate a pair of electrons ‘Nucleophile’ means ‘nucleus/positive charge loving’ as nucleophiles are attracted to positively charged species Nucleophilic refers to reactions that involve a nucleophile An electrophile is an electron-deficient species that can accept a pair of electrons ‘Electrophile’ means ‘electron/negative charge loving’ as electrophiles are attracted to negatively charged species Page 20 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Electrophilic refers to reactions that involve an electrophile YOUR NOTES A nucleophile ‘loves’ a positive charge and an electrophile ‘loves’ a negative charge Types of reactions An addition reaction is an organic reaction in which two (or more) molecules combine to give a single product with no other products A substitution reaction is a reaction that involves replacing an atom or group of atoms by another An elimination reaction is a reaction in which a small molecule (such as H2O or HCl) is removed from an organic molecule A hydrolysis reaction is a reaction in which a compound is broken down by water (it can also refer to the breakdown of a substance by dilute acids or alkali) A condensation reaction is a reaction in which two organic molecules join together and in the process eliminate small molecules (such as H2O or HCl) Page 21 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 22 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The different types of reactions in organic chemistry Oxidation & reduction An oxidation reaction is a reaction in which oxygen is added, electrons are removed or the oxidation number of a substance is increased In organic chemistry it often refers to the addition of oxygen or removal of hydrogen atoms to a substance In equations for organic redox reactions, the symbol [O] can be used to represent one atom of oxygen from an oxidising agent A reduction reaction is a reaction in which oxygen is removed, electrons are added or the oxidation number of a substance is decreased In organic chemistry it often refers to the removal of oxygen or addition of hydrogen atoms to a substance In equations for organic redox reactions, the symbol [H] can be used to represent one atom of hydrogen from a reducing agent Page 23 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES In organic chemistry oxidation is often the gain of oxygen or loss of hydrogen atoms and reduction is the gain of hydrogen and loss of oxygen atoms Page 24 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources 3.1.6 Terminology Used in Reaction Mechanisms Terminology Used in Reaction Mechanisms In organic reaction mechanisms, curly arrows represent the movement of electron pairs The arrow begins at a bond or a lone pair of electrons and points to the species that accepts the lone pair of electrons Curly arrows show electron pairs moving from the source (eg. a nucleophile) to its destination (eg. an electrophile) Free-radical substitution A free-radical substitution reaction is a reaction in which halogen atoms substitute for hydrogen atoms in alkanes It involves the initiation, propagation and termination steps Page 25 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Example of a free-radical substitution reaction to form chloromethane from methane Electrophilic addition An electrophilic addition reaction is a reaction in which an electron rich region in a molecule is attacked by an electrophile (a species that likes electrons/negative charge) followed by the addition of a small molecule to give one product only Page 26 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Example of an electrophilic addition reaction to form ethanol from ethene Nucleophilic substitution A nucleophilic substitution reaction is a reaction in which an electron-rich nucleophile displaces a halogen atom The general nucleophilic substitution reaction mechanism The C-X carbon of the halogenoalkane is electron deficient and has a δ+ charge The halogen atom, X, is more electronegative than the carbon atom which means that it pulls electrons towards itself and is δ– The nucleophile has a lone pair of electrons that it can donate to the δ+ carbon atom and form a covalent bond This causes the displacement of the halogen atom, X, which leaves as a halide ion, X– The displaced halide ion is known as a leaving group Nucleophilic addition A nucleophilic addition reaction is a reaction in which a nucleophile (a species that likes a nucleus/positive charge) attacks an electron-deficient region in a molecule followed by the addition of a small molecule to give one product only Page 27 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The general nucleophilic addition reaction mechanism Page 28 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources 3.1.7 Shapes of Organic Molecules; Sigma & Pi Bonds Straight, Branched & Cyclic Molecules Straight, branched and cyclic organic molecules are also called aliphatic compounds as long as they do not contain a benzene ring Straight-chain Straight-chain organic molecules are those in which the carbon atoms are connected to each other in one continuous chain Pentane is a straight-chain organic molecule as the carbon atoms are connected in a straight line Branched Branched organic molecules have side groups attached to the main chain of carbon atoms 2-methylbutane is a branched organic molecule as the main chain (consisting of 4 carbon atoms) has a methyl branch Cyclic Cyclic organic molecules are those in which the carbon atoms are connected to each other in a ring shape Page 29 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Cyclopentane is a cyclic organic molecule as the carbons are attached to each other in a ring structure Page 30 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.8 Hybridisation in Organic Molecules Hybridised Atoms: Shapes & Bond Angles in Molecules Each carbon atom has four electrons in its outer shell (electronic configuration: 1s22s22p2) Carbon atoms share these four electrons in four covalent bonds with other atoms to achieve a full outer shell configuration These electrons are found in orbitals within the respective atoms When forming a covalent bond, the orbitals overlap in such a way to form two types of bonds Sigma bonds (σ) Pi bonds (π) Hybridisation: sp3 The electron pair in a σ bond is found in a region of space between the nuclei of the two atoms that are sharing the electrons The electrostatic attraction between the electrons (negatively charged) and the two nuclei (positively charged) holds the two atoms together Carbon atoms that form four σ bonds are said to be sp3 hybridised The four pairs of electrons around each carbon repel each other forcing the molecule to adopt a configuration in which the bonding pairs of electrons are as far away from each other as possible The molecule adopts a tetrahedral arrangement with bond angles of 109.5 o The diagram shows a molecule of ethane in which each carbon atom forms four σ bonds to adopt a tetrahedral configuration and minimise the repulsion between the bonding pairs of electrons Hybridisation: sp2 When carbon atoms use only three of their electron pairs to form a σ bond, they are said to be sp2 hybridised Each carbon atom will have a p orbital with contains one spare electron When the p orbitals of two carbon atoms overlap with each other, a π bond is formed (the π bond contains two electrons) The two orbitals that form the π bond lie above and below the plane of the two carbon atoms to maximise bond overlap The three bonding pair of electrons are in the plane of the molecule and repel each other The molecule adopts a planar arrangement with bond angles of 120 o Page 31 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The overlap of the two p orbitals results in the formation of a π bond in ethene (sp2 hybridised molecule) in which the bonding pair of electrons repel each other to force the molecule into a planar configuration with bond angles of 120 o Hybridisation: sp Carbon atoms can also use only one of their electron pair to form a σ bond, in which case the carbon atoms are said to be sp hybridised Each carbon atom will have two p orbitals with one spare electron each When the four p orbitals of the carbon atoms overlap with each other, two π bonds are formed (each π bond contains two electrons) The two orbitals that form the π bond lie above and below the plane of the carbon atoms The two orbitals of the other π bond lie in front and behind the plane of the atoms This maximises the overlap of the four p orbitals The molecule adopts a linear arrangement with bond angles 180 o The overlap of the p orbitals results in the formation of two π bonds in ethyne (sp hybridised molecule) which adopts a linear arrangement with bond angles of 180 Page 32 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Tip Exam A double bond is a combination of a σ and π bond and a triple bond is a combination of one σ and two π bonds.The strength of the bonds increases as follows: single < double < triple bondThis is due to the increased electron density around the C-C atom, making the bond stronger and more difficult to break. Page 33 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Hybridised Atoms: σ and π Bonds in Molecules σ bonds Sigma bonds are formed from the end-on overlap of atomic orbitals S orbitals overlap this way as well as p orbitals Sigma orbitals can be formed from the end-on overlap of s or p orbitals The electron density in a σ bond is symmetrical about a line joining the nuclei of the atoms forming the bond The pair of electrons is found between the nuclei of the two atoms The electrostatic attraction between the electrons and nuclei bonds the atoms to each other The diagram below shows the arrangement of the σ bond in sp3, sp2 and sp hybridised carbon atoms Page 34 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES The σ orbitals are formed from the end-on overlap of the atomic orbitals resulting in symmetrical electron density on the atoms π bonds Pi (π) bonds are formed from the sideways overlap of p orbitals The two lobes that make up the π bond lie above and below the plane of the atoms This maximises overlap of the p orbitals Page 35 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES π orbitals can be formed from the end-on overlap of p orbitals In triple bonds, there is an additional overlap of p orbital The two lobes of the π bond lie in front of and behind the plane of the atoms in the molecule This maximises overlap of the p orbitals The diagram below shows the arrangement of the π bond in sp3, sp2 and sp hybridised carbon atoms Page 36 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The π orbitals are formed from the sideway overlap of the atomic orbitals Tip Exam π bonds are drawn as two electron clouds, one arising from each lobe of the p orbitals.The two clouds of electrons in a π bond represent one bond consisting of two electrons (one from each orbital). Page 37 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.9 Planarity of Organic Molecules Planar Molecules Planar molecules have all their atoms in the same plane Eg. linear, bent, trigonal planar and square planar Molecules which have all their atoms in the same plane The presence of an sp2 hybridised carbon can force the molecule to adopt a planar configuration (trigonal planar) The 3 σ bonds position themselves in a trigonal planar position so that the bonding pair of electrons are as far away from each other and therefore minimise the repulsion between them Eg. ethene Page 38 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Ethene is a planar molecule with two trigonal planar centres around the carbon atoms Eg. propene Page 39 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Propene has two trigonal planar centres around the carbon-carbon double bond and one tetrahedral centre The presence of an sp hybridised carbon can also force the molecule to adopt a planar configuration (linear) The 2 σ bonds position themselves in a linear position to minimise the repulsion between the bonding pairs of electrons For example, ethyne Ethyne is a planar molecule with one planar centre: the molecule is linear Eg. propyne Propyne has one planar centre around the carbon-carbon triple bond (linear) and one tetrahedral centre Page 40 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.10 Structural Isomerism Structural Isomerism: Chain, Position & Functional Group Structural isomers are compounds that have the same molecular formula but different structural formulae Eg. propene and cyclopropane Both propene and cyclopropane are made up of 3 carbon and 6 hydrogen atoms but the structure of the two molecules differs There are three different types of structural isomerism: Chain isomerism Positional isomerism Functional group isomerism Chain isomerism Chain isomerism is when compounds have the same molecular formula, but their longest hydrocarbon chain is not the same This is caused by branching Eg. pentane and 2,2-dimethylpropane Page 41 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Both compounds are made up of the same atoms however the longest carbon chain in pentane is 5 and in 2,2-dimethylpropane 3 (with two methyl branches) Positional isomerism Positional isomers arise from differences in the position of a functional group in each isomer The functional group can be located on different carbons For example, butanol and 2-butanol Both compounds have an alcohol group and are made up of 4 carbon, 10 hydrogen and one oxygen atom however in butanol the functional group is located on the first carbon and in 2butanol on the second carbon Functional group isomerism When different functional groups result in the same molecular formula, functional group isomers arise The isomers have very different chemical properties as they have different functional groups For example, butanol and ethoxyethane Page 42 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Both compounds have the same molecular formula however butanol contains an alcohol functional group and ethoxyethane an ether functional group Page 43 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.11 Stereoisomerism Stereoisomerism: Geometrical & Optical Stereoisomers are compounds that have the same atoms connected to each other, however the atoms are differently arranged in space There are two types of stereoisomerism: Geometrical (cis/trans) isomerism Optical isomerism Geometrical (cis/trans) isomerism Geometrical isomerism is seen in unsaturated (double bond containing) or ring compounds that have the same molecular formula and order of atoms (the atoms are connected similarly to each other) but different shapes Cis/trans nomenclature is used to distinguish between the isomers Cis isomers have functional groups on the same side of the double bond/carbon ring Trans isomers have functional groups on opposite sides of the double bond/carbon ring Geometrical isomerism in unsaturated compounds Page 44 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Geometrical isomerism in cyclic compounds This causes the compounds to have different chemical and physical properties For example, they may have different reaction rates for the same reaction (chemical property) or different melting/boiling points (physical property) Optical isomerism Optical isomers arise when a carbon atom in a molecule is bonded to four different atoms or groups of atoms The carbon atom is ‘asymmetric’ as there is no plane of symmetric in the molecule and is also called the chiral centre of the molecule The two different optical isomers are also called enantiomers Page 45 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Just like the left hand cannot be superimposed on the right hand, enantiomers too are non-superimposable Enantiomers are mirror images of each other Both molecules are made up of the same atoms which are bonded to each other identically, however the chiral centre (carbon with four different groups) gives rise to optical isomerism Optical isomers differ in their ability to rotate the plane of polarised light One enantiomer will rotate it clockwise and the other anticlockwise A2 only Normal light is unpolarised and consists of electric and magnetic fields that vibrate at right angles to each other in every possible direction When the unpolarised light passes through a polariser, the light gets polarised causing it to vibrate in only one plane A pair of optical isomers will rotate the plane of polarised light by equal amounts in opposite direction When equal amounts of the enantiomers are present in solution, the plane of polarised light doesn’t change As the enantiomers cancel out each other’s effect A solution with equal amounts of both enantiomers is also called a racemic mixture Page 46 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Light consists of vibrations in all possible directions however when it passes through a polariser the light gets polarised and vibrates in only one plane: enantiomers cause the plane of polarised light to rotate clockwise or anticlockwise Page 47 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Geometrical Isomerism in Alkenes Unsaturated compounds In unsaturated compounds, the groups attached to the C=C carbons remain fixed in their position This is because free rotation of the bonds about the C=C bond is not possible due to the presence of a π bond The presence of a π bond in unsaturated compounds restricts rotation about the C=C bond forcing the groups to remain fixed in their position and giving rise to the formation of geometrical isomers Page 48 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Tip Exam Geometrical isomerism is also possible in cyclic compounds because there is limited rotation about C-C single bonds that make up the rings.Therefore, the substitutions in cyclic compounds are fixed in their position (to stay either above or below the ring of carbon atoms). Page 49 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.12 Chirality Chirality & Enantiomers Chiral centres in non-cyclic molecules A chiral centre in a molecule is a carbon atom that has four different atoms or group of atoms attached This gives rise to two optical isomers which are also called enantiomers The enantiomers are mirror images of each other and cannot be superimposed The presence of the chiral centre in the molecule allows two enantiomers to exist which are stereoisomers as the molecules have the same atoms bonded to each other, but they are differently arranged in space When the molecule contains more than one chiral centre (asymmetric carbon) more than two optical isomers will be formed If there are two chiral centres, each chiral centre will rotate the plane of polarised light clockwise and anticlockwise There are four possible optical isomers Page 50 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Each chiral centre gives rise to two optical isomers; therefore, the molecule has a total of four optical isomers Chiral centres in cyclic molecules To determine the chiral centre in a cyclic molecule, the carbon bonded to four different atoms or groups of atoms should be found Eg. 1,2-aminocyclohexanol has two chiral centres so it can form four optical isomers Page 51 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES To decide where the chiral centres are in a cyclic molecule, the carbon atoms bonded to four different atoms or atom groups should be found Tip Exam Use a molecular modelling kit and make the models of enantiomers to help you understand that the two molecules are non-superimposable and therefore nonidentical. Page 52 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Identifying Chirality & Geometrical Isomerism Identify chirality Identifying chiral centres in cyclic and non-cyclic compounds is very straightforward as it is the carbon with four different atoms or atom groups in a molecule This gives rise to two optical isomers When more than two chiral centres are present, more than two optical isomers exist A molecule with three chiral centres will have six optical isomers A molecule containing chiral centres is called a chiral molecule Identifying geometrical isomers Molecules with restricted rotation about the C-C bond can have geometrical isomers This includes unsaturated and cyclic compounds Eg. alkenes and cyclopentane When the groups are positioned on the same side of the C-C double bond, the compound is a cis isomer When the groups are positioned on opposite sides of the C-C double bond the compound is a trans isomer Worked example: Drawing optical isomers Page 53 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Worked example: Drawing geometrical isomers Page 54 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 55 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 56 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.1.13 Isomers of Organic Compounds Deducing Isomers of a Compound You should be able to deduce all possible isomers for organic compounds knowing their molecular formula Worked example: Isomers of dibromopropane Step 1: Draw the structural formula of the compound Step 2: Determine whether it is a stereo or structural isomer There is no restricted bond rotation around the C-C bond and there is no chiral centre so it is structural isomerism Step 3: Determine whether it is a functional group, chain or positional isomerism Functional group? No, as Br is the only functional group possible Chain? No, as the longest chain can only be 3 Positional? Yes, as the two bromine atoms can be bonded to different carbon atoms Page 57 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Worked example: Deducing isomers of C4H10 Step 1: Draw the structural formula of the compound Step 2: Determine whether it is a stereo or structural isomer. Page 58 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources There is no restricted bond rotation around the C-C bond and there is no chiral centre so it is structural isomerism Step 3: Determine whether it is a functional group, chain or positional isomerism Functional group? No, as there are no functional groups Positional? No, as there are no functional groups which can be positioned on different carbon atoms Chain? Yes! Worked example: Deducing isomers of C2H2Cl2 Step 1: Draw the possible structural formula of the compound Page 59 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Step 2: Determine whether it is a stereo or structural isomer The compound has to be unsaturated for it to have molecular formula C2H2Cl2 ; Due to the double bond there is restricted rotation about the C-C bond; This compound will therefore display geometrical isomerism Step 3: Determine whether it is optical or geometrical isomerism Optical? No, as there are no chiral centres Geometric? Yes! Page 60 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2 Hydrocarbons 3.2.1 Alkanes Production of Alkanes: Hydrogenation & Cracking Alkanes are hydrocarbons that can be produced by the addition reaction of hydrogen to an alkene or by cracking of longer alkane chains Production of alkanes from addition reactions Alkenes are unsaturated organic molecules and contain C-C double bonds When hydrogen gas and an alkene are heated and passed over a finely divided Pt/Ni catalyst, the addition reaction produces an alkane: The Pt/Ni catalyst is finely divided to increase its surface area and therefore increase the rate of reaction Eg. butane from 1-butene Hydrogen gas is added to 1-butene which are then heated and passed over a Pt/Ni catalyst to produce butane The addition reaction of alkenes with hydrogen is called hydrogenation Hydrogenation is often used in the manufacture of margarine from vegetable oil Vegetable oil is an unsaturated organic molecule with many C-C double bonds When these are partially hydrogenated, their hydrocarbon chains become straighter This raises the melting point of the oils which is why margarine is a soft solid and vegetable oil a liquid at room temperature Production of alkanes from cracking In cracking large, less useful hydrocarbon molecules found in crude oil are broken down into smaller, more useful molecules The large hydrocarbon molecules are fed into a steel chamber and heated to a high temperature and then passed over an aluminium oxide (Al2O3) catalyst The chamber does not contain any oxygen to prevent combustion of the hydrocarbon to water and carbon dioxide When a large hydrocarbon is cracked, a smaller alkane and alkene molecules are formed Eg. octane and ethene from decane Page 61 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Long hydrocarbons are cracked by heating them and using aluminium oxide catalyst into smaller hydrocarbons and an alkene Tip Exam Remember that hydrogenation is an exothermic reaction and cracking is an endothermic reaction. Page 62 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources 3.2.2 Combustion & Free Radical Substitution of Alkanes Combustion & Free Radical Substitution of Alkanes Alkanes are combusted (burnt) on a large scale for their use as fuels They also react in free-radical substitution reactions to form more reactive halogenoalkanes Complete combustion When alkanes are burnt in excess (plenty of) oxygen, complete combustion will take place and all carbon and hydrogen will be oxidised to carbon dioxide and water respectively For example, the complete combustion of octane to carbon dioxide and water The complete combustion of alkanes Incomplete combustion When alkanes are burnt in only a limited supply of oxygen, incomplete combustion will take place and not all the carbon is fully oxidised Some carbon is only partially oxidised to form carbon monoxide For example, the incomplete combustion of octane to form carbon monoxide The incomplete combustion of alkanes Carbon monoxide is a toxic gas as it will bind to haemoglobin in blood which can then no longer bind oxygen As no oxygen can be transported around the body, victims will feel dizzy, lose consciousness and if not removed from the carbon monoxide, they can die Carbon monoxide is extra dangerous as it is odourless (it doesn’t smell) and will not be noticed Incomplete combustion often takes place inside a car engine due to a limited amount of oxygen present Page 63 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Free-radical substitution of alkanes Alkanes can undergo free-radical substitution in which a hydrogen atom gets substituted by a halogen (chlorine/bromine) Since alkanes are very unreactive, ultraviolet light (sunlight) is needed for this substitution reaction to occur The free-radical substitution reaction consists of three steps: In the initiation step, the halogen bond (Cl-Cl or Br-Br) is broken by UV energy to form two radicals These radicals create further radicals in a chain type reaction called the propagation step The reaction is terminated when two radicals collide with each other in a termination step Page 64 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.3 Free Radical Substitution Free Radical Substitution Mechanism Alkanes can undergo free-radical substitution in which a hydrogen atom gets substituted by a halogen (chlorine/bromine) Ultraviolet light (sunlight) is needed for this substitution reaction to occur The free-radical substitution reaction consists of three steps The fact that the bromine colour has disappeared only when mixed with an alkane and placed in sunlight suggests that the ultraviolet light is essential for the free radical substitution reaction to take place Initiation step In the initiation step the Cl-Cl or Br-Br is broken by energy from the UV light This produces two radicals in a homolytic fission reaction Page 65 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The first step of the free-radical substitution reaction is the initiation step in which two free radicals are formed by sunlight Propagation step The propagation step refers to the progression (growing) of the substitution reaction in a chain type reaction Free radicals are very reactive and will attack the unreactive alkanes A C-H bond breaks homolytically (each atom gets an electron from the covalent bond) An alkyl free radical is produced This can attack another chlorine/bromine molecule to form the halogenoalkane and regenerate the chlorine/bromine free radical This free radical can then repeat the cycle The second step of the free-radical substitution reaction is the propagation step in which the reaction grows in a chain type reaction Page 66 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources This reaction is not very suitable for preparing specific halogenoalkanes as a mixture of substitution products are formed If there is enough chlorine/bromine present, all the hydrogens in the alkane will eventually get substituted (eg. ethane will become C2Cl6/C2Br6) The free-radical substitution reaction gives a variety of products and not a pure halogenoalkane Termination step The termination step is when the chain reaction terminates (stops) due to two free radicals reacting together and forming a single unreactive molecule Multiple products are possible The final step in the substitution reaction to form a single unreactive molecule Page 67 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Tip Exam You could be asked to draw the mechanism for initiation and termination steps for free radical substitution. This mechanism will uses half headed arrows to show the movement of one electron (double headed arrows show the movement of a pair of electrons). A half headed arrow is known as a ‘fish hook’ arrow. Initiation: Termination: The key is the use of the ‘fish hook’ arrow to show the homolytic fission of the bond in initiation and the formation of the bond in termination. Page 68 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.4 Cracking of Alkanes Obtaining Useful Compounds by Cracking Crude oil Crude oil is a mixture of hydrocarbons containing alkanes, cycloalkanes and arenes (compounds with a benzene ring) The crude oil is extracted from the earth in a drilling process and transported to an oil refinery At the oil refinery the crude oil is separated into useful fuels by fractional distillation This is a separating technique in which the wide range of different hydrocarbons are separated into fractions based on their boiling points Crude oil is initially separated into fractions with similar boiling points in a process called fractional distillation However, the smaller hydrocarbon fractions (such as gasoline fractions) are in high demand compared to the larger ones Therefore, some of the excess heavier fractions are broken down into smaller, more useful compounds Page 69 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources These more useful compounds include alkanes and alkenes of lower relative formula mass (Mr) This process is called cracking The heavier fractions that are obtained in fractional distillation are further cracked into useful alkane and alkenes with lower Mr values Cracking The large hydrocarbon molecules are fed into a steel chamber and heated to a high temperature and then passed over an aluminium oxide (Al2O3) catalyst The chamber does not contain any oxygen to prevent combustion of the hydrocarbon to water and carbon dioxide When a large hydrocarbon is cracked, a smaller alkane and alkene molecules are formed Eg. octane and ethene from decane Long hydrocarbon fraction is cracked into two smaller ones The low-molecular mass alkanes formed make good fuels and are in high demand Page 70 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources The low-molecular mass alkenes are more reactive than alkanes due to their double bond This makes them useful for the chemical industry as the starting compounds (feedstock) for making new products Eg. they are used as monomers in polymerisation reactions Alkenes are reactive molecules and can undergo many different types of reactions making them useful as starting compounds Page 71 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.5 Chemical Reactivity of Alkanes Unreactivity of Alkanes Strength of C-H bonds Alkanes consist of carbon and hydrogen atoms which are bonded together by single bonds Unless a lot of heat is supplied, it is difficult to break these strong C-C and C-H covalent bonds This decreases the alkanes’ reactivities in chemical reactions Lack of polarity The electronegativities of the carbon and hydrogen atoms in alkanes are almost the same This means that both atoms share the electrons in the covalent bond almost equally The Pauling Scale shows that the difference in electronegativity between carbon and hydrogen is only 0.4 As a result of this, alkanes are nonpolar molecules and have no partial positive or negative charges (δ+ and δ- respectively) Alkanes therefore do not react with polar reagents They have no electron-deficient areas to attract nucleophiles And also lack electron-rich areas to attract electrophiles Page 72 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Ethane is an example of an alkane that lacks polarity due to almost similar electronegativities of the carbon and hydrogen atoms Due to the unreactivity of alkanes, they only react in combustion reactions and undergo substitution by halogens Tip Exam Remember: nucleophiles are negatively charged and are attracted to electron- deficient regions.Electrophiles are positively charged and attracted to electron-rich regions. Page 73 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.6 Combustion of Alkanes Combustion of Alkanes & the Environment Cars’ exhaust fumes include toxic gases such as carbon monoxide (CO), oxides of nitrogen (NO/NO2) and volatile organic compounds (VOCs) When released into the atmosphere, these pollutants have drastic environmental consequences damaging nature and health Carbon monoxide Carbon monoxide is formed in the incomplete combustion of alkanes inside a car engine Due to lack of enough oxygen in the engine, some of the carbon is only partially oxidised to CO instead of carbon dioxide (CO2) Incomplete combustion of alkanes is caused by a limited supply of oxygen CO is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death The CO binds to haemoglobin which therefore cannot bind oxygen and carbon dioxide Oxygen is transported to organs Carbon dioxide is removed as waste material from organs Page 74 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources The high affinity of CO to haemoglobin prevents it from binding to O2 and CO2 Oxides of nitrogen YOUR NOTES Normally, nitrogen is too unreactive to react with oxygen in air However, in a car’s engine, high temperatures and pressures are reached causing the oxidation of nitrogen to take place: N2(g) + O2(g) → 2NO(g) N2(g) + 2O2(g) → 2NO2(g) The oxides of nitrogen are then released in the car’s exhaust fumes into the atmosphere Car exhaust fumes also contain unburnt hydrocarbons from fuels and their oxides (VOCs) In air, the nitrogen oxides can react with these VOCs to form peroxyacetyl nitrate (PAN) which is the main pollutant found in photochemical smog PAN is also harmful to the lungs, eyes and plant-life Nitrogen oxides can also dissolve and react in water with oxygen to form nitric acid which is a cause of acid rain Acid rain can cause corrosion of buildings, endangers plant and aquatic life (as lakes and rivers become too acidic) as well as directly damaging human health Catalytic removal To reduce the amount of pollutants released in cars’ exhaust fumes, many cars are now fitted with catalytic converters Precious metals (such as platinum) are coated on a honeycomb to provide a large surface area The reactions that take place in the catalytic converter include: Oxidation of CO to CO2: 2CO + O2 → 2CO2 or 2CO + 2NO → 2CO2 + N2 Reduction of NO/NO2 to N2: 2CO + 2NO → 2CO2 + N2 Oxidation of unburnt hydrocarbons: CnH2n+2 + (3n+1)[O] → nCO2 + (n+1)H2O Pollutants, their effect & removal table Page 75 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Tip Exam Though CO is not a toxic gas, it is still a pollutant causing global warming and 2 climate change. Page 76 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.7 Production of Alkenes Production of Alkenes: Elimination, & Dehydration Reactions & Cracking Alkenes can be made by a series of reactions including elimination, dehydration reactions and cracking Elimination reaction Alkenes can be produced from the elimination reaction of a halogenoalkane An elimination reaction is one in which a small molecule is lost In the case of halogenoalkanes, the small molecule that is eliminated is a hydrogen halide, HX, where X is the halogen The halogenoalkane is heated with ethanolic sodium hydroxide Production of an alkene from a halogenoalkane by reacting it with ethanolic sodium hydroxide and heating it The eliminated H+ in HBr reacts with the ethanolic OH- to form water The eliminated Br- in HBr reacts with Na+ to form NaBr Page 77 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The eliminated HBr reacts with ethanolic OH- and Na+ to form H2O and NaBr Note that the reaction conditions should be stated correctly as different reaction conditions will result in different types of organic reactions NaOH (ethanol): an elimination reaction occurs to form an alkene NaOH (aq): a nucleophilic substitution reaction occurs, and an alcohol is one of the products Page 78 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Different reaction conditions will give different products Dehydration reaction Alkenes can also be produced from the elimination reaction of alcohols in which a water molecule is lost This is also called a dehydration reaction Alcohol vapour is passed over a hot catalyst of aluminium oxide powder (Al2O3) Concentrated acid, pieces of porous pot or pumice can also be used as catalysts Production of an alkene from an alcohol by using a hot aluminium oxide powder catalyst Page 79 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The formation of ethene from ethanol is an example of a dehydration reaction of alcohols The smaller alkenes (such as ethene, propene and butene) are all gases at room temperature and can be collected over water The smaller alkenes are gases at room temperature and collected over water Cracking Alkenes can also be produced from the cracking of long hydrocarbon molecules in crude oil An aluminium oxide (Al2O3) catalyst and high temperatures are used to speed up this reaction. It is important to ensure that the crude oil doesn’t come into contact with oxygen as this can cause combustion of the hydrocarbons to produce water and carbon dioxide Page 80 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources The cracking of crude oil produces a smaller alkane and alkene molecules YOUR NOTES Long hydrocarbon fraction is cracked into two smaller ones The low-molecular mass alkenes are more reactive than alkanes as they have an electronrich double bond They can therefore be used as feedstock for making new products Alkenes are reactive molecules and can undergo many different types of reactions making them useful as starting compounds Page 81 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.8 Reactions of Alkenes Reactions of Alkenes Alkenes are very useful compounds as they can undergo many types of reactions They can therefore be used as starting molecules when making new compounds Electrophilic addition Electrophilic addition is the addition of an electrophile to a double bond The C-C double bond is broken, and a new single bond is formed from each of the two carbon atoms Electrophilic addition reactions include the addition of: Hydrogen (also known as hydrogenation reaction) Steam (H2O (g)) Hydrogen halide (HX) Halogen Page 82 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The diagram shows an overview of the different electrophilic addition reactions alkenes can undergo Oxidation Alkenes can also be oxidised by acidified potassium manganate(VII) (KMnO4) which is a very powerful oxidising agent Alkenes can be oxidised by both hot and cold KMnO4 which will result in different products being formed When shaken with cold dilute KMnO4 the pale purple solution turns colourless and the product is a diol Page 83 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources When alkenes are reacted with hot concentrated KMnO4 the conditions are harsher causing the C-C double bond to completely break The O-H groups in the diol formed are further oxidised to ketones, aldehydes, carboxylic acids or carbon dioxide gas The actual products formed depend on what is bonded to the carbon atoms in the alkene Alkenes can be oxidised by cold dilute and hot concentrated KMnO4 to give different products Page 84 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources The reactions of alkenes with hot concentrated KMnO4 can be used to determine the position of the double bond in larger alkenes The above reactions can be used to predict where the double bond in a larger molecule is Worked example: Oxidation of alkenes Answer The products are propanone (a ketone), carbon dioxide and water. Page 85 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Worked example: Identifying alkenes from oxidation reactions Answer The alkene is 1-butene. Addition polymerisation Addition polymerisation is the reaction of many monomers containing at least one double C-C bond to form the long-chain polymers as the only product Monomers are small, reactive molecules that react together to make the polymer A polymer is a long-chain molecule made up of many repeating units (monomers) In addition polymerisation reaction, the C-C double bond is broken to link together the monomers and form a polymer This is a common method to make plastics Page 86 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The diagram shows a polymerisation reaction of ethene to poly(ethene) Page 87 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The diagram shows a polymerisation reaction of propene to poly(propene) Other alkenes and substituted alkenes can also polymerise to make polymers with different properties Eg. poly(chloroethene), also known as PVC is the most versatile plastic used Page 88 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Poly(chloroethene) is used as plastic YOUR NOTES Page 89 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.9 Test for Unsaturation Test for Unsaturation Halogens can be used to test if a molecule is unsaturated (i.e. contains a double bond) Br2(aq) is an orange or yellow solution, called bromine water and this is the halogen most commonly used The unknown compound is shaken with the bromine water If the compound is unsaturated, an addition reaction will take place and the coloured solution will decolourise The decolourisation of bromine water by an unsaturated compound as a result of an addition reaction Page 90 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.10 Electrophilic Addition of Alkenes Alkenes: Electrophilic Addition The double bond in alkenes is an area of high electron density (there are four electrons found in this double bond) This makes the double bond susceptible to attack by electrophiles (electron-loving species) An electrophilic addition is the addition of an electrophile to a double bond Electrophilic addition of hydrogen bromide A molecule of hydrogen bromide (HBr) is polar as the hydrogen and bromine atoms have different electronegativities The bromine atom has a stronger pull on the electrons in the H-Br bond As a result of this, the Br atom has a partial negative and the H atom a partial positive charge Due to differences in electronegativities of the hydrogen and bromine atom, HBr is a polar molecule In an addition reaction, the H atom acts as an electrophile and accepts a pair of electrons from the C-C bond in the alkene The H-Br bond breaks heterolytically, forming a Br- ion This result in the formation of a highly reactive carbocation intermediate which reacts with the Br- (nucleophile) Page 91 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Example of an electrophilic addition reaction of HBr and propene to form 1-bromopropane and 2-bromopropane Electrophilic addition of bromine Bromine (Br2) is a non-polar molecule as both atoms have similar electronegativities and therefore equally share the electrons in the covalent bond However, when a bromine molecule gets closer to the double bond of an alkene, the high electron density in the double bond repels the electron pair in Br-Br away from the closest Br atom As a result of this, the closest Br atom to the double bond is slightly positive and the further Br atom is slightly negatively charged Page 92 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Br2 is a non-polar molecule however when placed close to an area of high electron density it can get polarised In an addition reaction, the closest Br atom acts as an electrophile and accepts a pair of electrons from the C-C bond in the alkene The Br-Br bond breaks heterolytically, forming a Br- ion This results in the formation of a highly reactive carbocation intermediate which reacts with the Br- (nucleophile) Example of an electrophilic addition reaction of Br2 and ethene to form dibromoethane Tip Exam The stability of the carbocation intermediate is as follows:tertiary > secondary > primaryWhen more than one carbocations can be formed, the major product of the reaction will be the one that results from the nucleophilic attack of the most stable carbocation. Page 93 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.2.11 Markovnikov's Rule Alkenes: Stability of Cations & Markovnikov's Rule Carbocations are positively charged carbon atoms with only three covalent bonds instead of four There are three types of carbocations: primary, secondary and tertiary Inductive effect The alkyl groups attached to the positively charged carbon atoms are ‘electron donating groups’ This is also known as the inductive effect of alkyl groups The inductive effect is illustrated by the use of arrowheads on the bonds The alkyl groups push electrons away from themselves towards the positively charged carbon This causes the carbocation to become less positively charged As a result of this, the charge is spread around the carbocation which makes it energetically more stable This means that tertiary carbocations are the most stable as they have three electrondonating alkyl groups which energetically stabilise the carbocation Due to the positive charge on the carbon atom, carbocations are electron-loving species (electrophiles) Alkyl groups push electron density towards the carbocation making it energetically more stable; the more alkyl groups the carbocation is bonded to, the more stabilised it is Markovnikov’s rule In addition reactions, an electrophile reacts with the double bond of alkenes Page 94 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The electrophile reacts with the electron-rich C-C double bond The electrophile will add to the carbon to give the most stable carbocation The most stable carbocation is the major product of the nucleophilic attack on the C-C double bond Therefore, the nucleophile will bond to the C-C carbon atom with the highest number of alkyl groups bonded to it The nucleophile ends up to the most substituted C-C carbon atom Page 95 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES This is also known as the Markovnikov’s rule which predicts the outcome of addition reactions and states that: In an addition reaction of a halogen halide (HX) to an alkene, the halogen ends up bonded to the most substituted carbon atom. Page 96 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.3 Halogen Compounds 3.3.1 Production of Halogenoalkanes Production of Halogenoalkanes: Substitution & Addition Reactions Halogenoalkanes are alkanes that have one or more halogens They can be produced from: Free-radical substitution of alkanes Electrophilic addition of alkenes Substitution of an alcohol Free-radical substitution of alkanes Ultraviolet light (UV) is required for the reaction to start off A free-radical substitution reaction is a three-step reaction consisting of initiation, propagation and termination steps In the initiation step the halogen bond is broken by energy from the UV light to produce two radicals in a homolytic fission reaction The propagation step refers to the progression (growing) of the substitution reaction in a chain type reaction The termination step is when the chain reaction terminates (stops) due to two free radicals reacting together and forming a single unreactive molecule Page 97 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Free-radical substitution reactions of alkanes produce halogenoalkanes Electrophilic addition Halogenoalkanes can also be produced from the addition of hydrogen halides (HX) or halogens (X2) at room temperature to alkenes In hydrogen halides, the hydrogen acts as the electrophile and accepts a pair of electrons from the C-C bond in the alkene The major product is the one in which the halide is bonded to the most substituted carbon atom (Markovnikov’s rule) In the addition of halogens to alkenes, one of the halogen atoms acts as an electrophile and the other as a nucleophile Page 98 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Electrophilic addition of hydrogen halides or hydrogen at room temperatures to alkenes results in the formation of halogenoalkanes Substitution of alcohols In the substitution of alcohols an alcohol group is replaced by a halogen to form a halogenoalkane The subustition of the alcohol group for a halogen can be achieved by reacting the alcohol with: HX (or KBr with H2SO4 or H3PO4 to make HX) PCl3 and heat PCl5 at room temperature SOCl2 Page 99 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Substitution of alcohols to produce halogenoalkanes Page 100 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Overview of the different ways to produce halogenoalkanes Page 101 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Classifying Halogenoalkanes YOUR NOTES Depending on the carbon atom the halogen is attached to, halogenoalkanes can be classified as primary, secondary and tertiary A primary halogenoalkane is when a halogen is attached to a carbon that itself is attached to one other alkyl group A secondary halogenoalkane is when a halogen is attached to a carbon that itself is attached to two other alkyl groups A tertiary halogenoalkane is when a halogen is attached to a carbon that itself is attached to three other alkyl groups Primary, secondary and tertiary halogenoalkanes Page 102 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources 3.3.2 Substitution Reactions of Halogenoalkanes Nucleophilic Substitution Reactions of Halogenoalkanes Halogenoalkanes are much more reactive than alkanes due to the presence of the electronegative halogens The halogen-carbon bond is polar causing the carbon to carry a partial positive and the halogen a partial negative charge A nucleophilic substitution reaction is one in which a nucleophile attacks a carbon atom which carries a partial positive charge An atom that has a partial negative charge is replaced by the nucleophile Due to large differences in electronegativity between the carbon and halogen atom, the CX bond is polar Reaction with NaOH The reaction of a halogenoalkane with aqueous alkali results in the formation of an alcohol The halogen is replaced by the OHThe aqueous hydroxide (OH- ion) behaves as a nucleophile by donating a pair of electrons to the carbon atom bonded to the halogen Hence, this reaction is a nucleophilic substitution For example, bromoethane reacts with aqueous alkali when heated to form ethanol The halogen is replaced by a nucleophile, OH- Reaction with KCN The nucleophile in this reaction is the cyanide, CN- ion Ethanolic solution of potassium cyanide (KCN in ethanol) is heated under reflux with the halogenoalkane The product is a nitrile Page 103 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources For example, bromoethane reacts with ethanolic potassium cyanide when heated under reflux to form propanenitrile The halogen is replaced by a cyanide group, CNThe nucleophilic substitution of halogenoalkanes with KCN adds an extra carbon atom to the carbon chain This reaction can therefore be used by chemists to make a compound with one more carbon atom than the best available organic starting material Reaction with NH3 The nucleophile in this reaction is the ammonia, NH3 molecule An ethanolic solution of excess ammonia (NH3 in ethanol) is heated under pressure with the halogenoalkane The product is a primary amine For example, bromoethane reacts with excess ethanolic ammonia when heated under pressure to form ethylamine The halogen is replaced by an amine group, NH3 It is very important that the ammonia is in excess as the product of the nucleophilic substitution reaction, the ethylamine, can act as a nucleophile and attack another bromoethane to form the secondary amine, diethylamine Reaction with aqueous silver nitrate Halogenoalkanes can be broken down under reflux by water to form alcohols The breakdown of a substance by water is also called hydrolysis This reaction is classified as a nucleophilic substitution reaction with water molecules in aqueous silver nitrate solution acting as nucleophiles, replacing the halogen in the halogenoalkane For example, bromoethane reacts with aqueous silver nitrate solution to form ethanol Page 104 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES The halogen is replaced by a hydroxyl group, OHThis reaction is similar to the nucleophilic substitution reaction of halogenoalkanes with aqueous alkali, however, hydrolysis with water is much slower than with the OH- ion in alkalis The hydroxide ion is a better nucleophile than water as it carries a full formal negative charge In water, the oxygen atom only carries a partial negative charge A hydroxide ion is a better nucleophile as it has a full formal negative charge whereas the oxygen atom in water only carries a partial negative charge; this causes the nucleophilic substitution reaction with water to be much slower than with aqueous alkali The halogenoalkanes have different rates of hydrolysis, so this reaction can be used as a test to identify halogens in a halogenoalkane by measuring how long it takes for the test tubes containing the halogenoalkane and aqueous silver nitrate solutions to become opaque Page 105 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources 3.3.3 Elimination Reactions of Halogenoalkanes Halogenoalkanes: Elimination Reactions In an elimination reaction, an organic molecule loses a small molecule In the case of halogenoalkanes this small molecule is a hydrogen halide (eg. HCl) The halogenoalkanes are heated with ethanolic sodium hydroxide causing the C-X bond to break heterolytically, forming an X- ion and leaving an alkene as an organic product For example, bromoethane reacts with ethanolic sodium hydroxide when heated to form ethene Hydrogen bromide is eliminated to form ethene Tip Exam The reaction conditions in a reaction are extremely important.If NaOH(ethanol) is used, an elimination reaction takes place to form an alkene from a halogenoalkane.If NaOH(aq) is used, a nucleophilic substitution reaction takes place to form an alcohol from a halogenoalkane. Page 106 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.3.4 SN1 & SN2 Halogenoalkanes: SN1 & SN2 Mechanisms In nucleophilic substitution reactions involving halogenoalkanes, the halogen atom is replaced by a nucleophile These reactions can occur in two different ways (known as SN2 and SN1 reactions) depending on the structure of the halogenoalkane involved SN2 reactions In primary halogenoalkanes, the carbon that is attached to the halogen is bonded to one alkyl group These halogenoalkanes undergo nucleophilic substitution by an SN2 mechanism ‘S’ stands for ‘substitution’ ‘N’ stands for ‘nucleophilic’ ‘2’ means that the rate of the reaction (which is determined by the slowest step of the reaction) depends on the concentration of both the halogenoalkane and the nucleophile ions The SN2 mechanism is a one-step reaction The nucleophile donates a pair of electrons to the δ+ carbon atom to form a new bond At the same time, the C-X bond is breaking and the halogen (X) takes both electrons in the bond (heterolytic fission) The halogen leaves the halogenoalkane as an X- ion For example, the nucleophilic substitution of bromoethane by hydroxide ions to form ethanol Page 107 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The mechanism of nucleophilic substitution in bromoethane which is a primary halogenoalkane SN1 reactions In tertiary halogenoalkanes the carbon that is attached to the halogen is bonded to three alkyl groups These halogenoalkanes undergo nucleophilic substitution by an SN1 mechanism ‘S’ stands for ‘substitution’ ‘N’ stands for ‘nucleophilic’ ‘1’ means that the rate of the reaction (which is determined by the slowest step of the reaction) depends on the concentration of only one reagent, the halogenoalkane The SN1 mechanism is a two-step reaction In the first step, the C-X bond breaks heterolytically and the halogen leaves the halogenoalkane as an X- ion (this is the slow and rate-determining step) This forms a tertiary carbocation (which is a tertiary carbon atom with a positive charge) In the second step, the tertiary carbocation is attacked by the nucleophile For example, the nucleophilic substitution of 2-bromo-2-methylpropane by hydroxide ions to form 2-methyl-2-propanol Page 108 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The mechanism of nucleophilic substitution in 2-bromo-2-methylpropane which is a tertiary halogenoalkane Carbocations In the SN1 mechanism, a tertiary carbocation is formed This is not the case for SN2 mechanisms as a primary carbocation would have been formed which is much less stable than tertiary carbocations This has to do with the positive inductive effect of the alkyl groups attached to the carbon which is bonded to the halogen atom The alkyl groups push electron density towards the positively charged carbon, reducing the charge density In tertiary carbocations, there are three alkyl groups stabilising the carbocation whereas in primary carbocations there is only one alkyl group This is why tertiary carbocations are much more stable than primary ones The diagram shows the trend in stability of primary, secondary and tertiary carbocations Secondary halogenoalkanes undergo a mixture of both SN1 and SN2 reactions depending on their structure Page 109 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.3.5 Reactivity of Halogenoalkanes Reactivity of Halogenoalkanes The halogenoalkanes have different rates of substitution reactions Since substitution reactions involve breaking the carbon-halogen bond the bond energies can be used to explain their different reactivities Halogenoalkane Bond Energy Table The table above shows that the C-I bond requires the least energy to break, and is therefore the weakest carbon-halogen bond During substitution reactions the C-I bond will therefore heterolytically break as follows: R3C-I + OH- → R3C-OH + Ihalogenoalkane alcohol The C-F bond, on the other hand, requires the most energy to break and is, therefore, the strongest carbon-halogen bond Fluoroalkanes will therefore be less likely to undergo substitution reactions Aqueous silver nitrate Reacting halogenoalkanes with aqueous silver nitrate solution will result in the formation of a precipitate The rate of formation of these precipitates can also be used to determine the reactivity of the halogenoalkanes Halogenoalkane Precipitates Table Page 110 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The formation of the pale yellow silver iodide is the fastest (fastest nucleophilic substitution reaction) whereas the formation of the silver fluoride is the slowest (slowest nucleophilic substitution reaction) This confirms that fluoroalkanes are the least reactive and iodoalkanes are the most reactive halogenoalkanes The trend in reactivity of halogenoalkanes Page 111 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.4 Hydroxy Compounds 3.4.1 Production of Alcohols Production of Alcohols Alcohols are compounds that contain at least one hydroxy (-OH) group The general formula of alcohols is CnH2n+1OH Alcohols can be prepared by a wide range of chemical reactions Electrophilic addition of alkenes When hot steam is reacted with an alkene, using concentrated phosphoric(VI) acid (H3PO4)as a catalyst, electrophilic addition takes place to form an alcohol Electrophilic addition of steam to alkenes to form an alcohol Oxidation of alkenes Cold, dilute KMnO4 is a mild oxidising agent and oxidises alkenes The C-C double bond is not fully broken and a diol is formed A diol is a compound with two hydroxy, -OH, groups Oxidation of alkenes using cold, dilute KMnO4 to form a diol Nucleophilic substitution of halogenoalkanes The halide atom in halogenoalkanes can be substituted when heated with aqueous NaOH in a nucleophilic substitution reaction Page 112 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Nucleophilic substitution of halogenoalkanes using NaOH to form an alcohol Reduction of aldehyde & ketones Aldehydes and ketones can be reduced by reducing agents such as NaBH4 or LiAlH4 Aldehydes are reduced to primary alcohols The carbon attached to the hydroxy group is bonded to one other alkyl group Ketones are reduced to secondary alcohols The carbon attached to the hydroxy group is bonded to two other alkyl groups Reduction of aldehydes and ketones to form primary and secondary alcohols Reduction of carboxylic acids Similarly, carboxylic acids are reduced by NaBH4 or LiAlH4 to primary alcohols Page 113 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Reduction of carboxylic acids to primary alcohols Hydrolysis of ester Esters are made by a condensation reaction between an alcohol and a carboxylic acid When an ester is heated with dilute acid or alkali, hydrolysis will take place and the carboxylic acid and alcohol will be reformed Hydrolysis of esters to form alcohols Alcohol production reactions table Tip Exam The symbol [O] is used to represent oxygen provided by an oxidising agent. Page 114 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.4.2 Reactions of Alcohols Reactions of Alcohols Alcohols are reactive molecules which undergo a wide range of reactions Combustion of alcohols Alcohols react with oxygen in the air when ignited and undergo complete combustion to form carbon dioxide and water Alcohol + oxygen → carbon dioxide + water Complete combustion of alcohols to produce carbon dioxide and water Substitution of alcohols In the substitution of alcohols, a hydroxy group (-OH) is replaced by a halogen to form an halogenoalkane The substitution of the alcohol group for a halogen can be achieved by reacting the alcohol with: HX (rather than using HBr, KBr is reacted with H2SO4 or H3PO4 to make HBr that will then react with the alcohol) PCl3 and heat PCl5 at room temperature SOCl2 Page 115 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Substitution of alcohols to produce halogenoalkanes Reaction with Na When an alcohol reacts with a reactive metal such as sodium (Na), the oxygen-hydrogen bond in the hydroxy group breaks Though the reaction is less vigorous than sodium reacting with water, hydrogen gas is given off and a basic compound (alkoxide) is formed If the excess ethanol is evaporated off after the reaction a white crystalline solid of sodium alkoxide is left Alcohol + sodium → sodium alkoxide + hydrogen The longer the hydrocarbon chain in the alcohol, the less vigorous the reaction becomes Page 116 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Alcohols react with Na to form a basic sodium alkoxide salt and hydrogen gas Oxidation of alcohols Primary alcohols can be oxidised to form aldehydes which can undergo further oxidation to form carboxylic acids Secondary alcohols can be oxidised to form ketones only Tertiary alcohols do not undergo oxidation The oxidising agents of alcohols include acidified K2Cr2O7 or acidified KMnO4 Acidified potassium dichromate(VI), K2Cr2O7, is an orange oxidising agent Acidified means that that the potassium dichromate(VI) is in a solution of dilute acid (such as dilute sulfuric acid) For potassium dichromate(VI) to act as an oxidising agent, it itself needs to be reduced This reduction requires hydrogen (H+) ions which are provided by the acidic medium When alcohols are oxidised the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions Acidified potassium manganate(VII), KMnO4, is a purple oxidising agent As with acidified K2Cr2O7 the potassium manganate(VII) is in an acidic medium to allow reduction of potassium manganate(VII) to take place When alcohols are oxidised, the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions Warm primary alcohol is added to the oxidising agent The formed aldehyde has a lower boiling point than the alcohol reactant so it can be distilled off as soon as it forms If the aldehyde is not distilled off, further refluxing with excess oxidising agent will oxidise it to a carboxylic acid Since ketones cannot be further oxidised, the ketone product does not need to be distilled off straight away after it has been formed Page 117 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Oxidation of ethanol by acidified K2Cr2O7 to form an aldehyde by distillation and carboxylic acid by refluxing Oxidation of propan-2-ol by acidified K2Cr2O7 to form a ketone by distillation Dehydration of alcohols Alcohols can also undergo dehydration to form alkenes Dehydration is a reaction in which a water molecule is removed from a larger molecule A dehydration reaction is a type of elimination reaction Page 118 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Alcohol vapour is passed over a hot catalyst of aluminium oxide (Al2O3) powder OR pieces of porous pot or pumice as well as concentrated acid can be used as catalysts Dehydration of ethanol using aluminium oxide as a catalyst forms ethene gas, which can be collected over water Esterification of Alcohols Esterification is a condensation reaction between a carboxylic acid and an alcohol to form an ester and a water molecule For esterification to take place, the carboxylic acid and alcohol are heated under reflux with a strong acid catalyst (such as H2SO4 or H3PO4) Carboxylic acid + alcohol → ester + water The reaction is reversible so an equilibrium mixture can be established with all the reactants and products Esters have sweet, fruity smells Page 119 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Esterification of ethanol and ethanoic acid using a strong acid catalyst to form ethyl ethanoate and water Tip Exam The first part of an ester’s name comes from the alcohol, whereas the second part comes from the carboxylic acid.So, if ethanol and propanoic acid react together, this will make the ester ethyl propanoate. Page 120 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.4.3 Classifying and Testing for Alcohols Classifying Alcohols Primary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to one other carbon atom (or alkyl group) Secondary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to two other carbon atoms (or alkyl groups) Tertiary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to three other carbon atoms (or alkyl groups) Classifying primary, secondary and tertiary alcohols and alcohols with more than one alcohol group Only primary and secondary alcohols can get oxidised when mildly oxidised with acidified K2Cr2O7 Primary alcohols get mildly oxidised to aldehydes Secondary alcohols get mildly oxidized to ketones Tertiary alcohols do not undergo oxidation with acidified K2Cr2O7 Therefore, only the oxidation of primary and secondary alcohols will change the colour of K2Cr2O7 solution as the orange Cr2O72- ions are reduced to green Cr3+ ions Page 121 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Only propan-1-ol and propan-2-ol, which are primary and secondary alcohols respectively, can get oxidised, turning the orange solution green; no colour change is observed with 2-methyl-propan-2-ol, which is a tertiary alcohol Page 122 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Test for Alcohols YOUR NOTES Tri-iodomethane (also called iodoform) forms a yellow precipitate with methyl ketones Methyl ketones are compounds that have a CH3CO-group Ethanal also contains a CH3CO- group and therefore also forms a yellow precipitate with iodoform The reagent is heated with an alkaline solution of iodine This reaction involves a halogenation and hydrolysis step In the halogenation step, all three H-atoms in the -CH3 (methyl) group are replaced for iodine atoms, forming -CI3 The intermediate compound is hydrolysed by alkaline solution to form a sodium salt (RCO2- Na+) and a yellow precipitate of CHI3 The reaction of methyl ketones with iodoform results in the formation of a yellow CHI3 precipitate Iodoform & alcohols The position of a secondary alcohol can be deduced by reacting the compound with alkaline I2 If the -OH group is on the carbon atom next to a methyl group, it will firstly get oxidised to CH3CH(OH)- by the alkaline solution This will result in the formation of a methyl ketone RCOCH3 The methyl ketone will then first get halogenated and then hydrolysed to form the sodium salt and the yellow precipitate If no yellow precipitate is formed, then this means that the secondary alcohol is not on a carbon next to a methyl group Page 123 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The secondary alcohol butan-2-ol will firstly get oxidised to the methyl ketone butanone which will form a yellow precipitate when reacted with alkaline I2 Page 124 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.4.4 Alcohol Dissociation Acidity of Alcohols Alcohols have a low degree of dissociation This means, that when dissolved in water, alcohol molecules do not dissociate (split up) to a great extent ROH (aq) ⇄ RO- (aq) + H+ (aq) Alcohol alkoxide ion The position of the equilibrium lies to the left, meaning that there are far more alcohol molecules than RO- and H+ ions When water dissociates, the position of the equilibrium still lies to the left, but there are more H+ ions compared to the dissociation of alcohols H2O (l) ⇄ OH- (aq) + H+ (aq) As alcohols have a lower [H+ (aq)] in solution compared to water, alcohols are weaker acids than water The inductive effect in alcohols Electron-donating species such as alkyl groups push electrons into a covalent bond and are said to have a positive inductive effect In alcohols, the oxygen atom in the alkoxide ion is bonded to an electron-donating alkyl group This means that there is more electron density on the O- atom The alkoxide ion is, therefore, more likely to accept an H+ ion and form the alcohol again Alkyl groups in the alkoxide ion donate electron density to the negatively charged oxygen, causing it to more readily accept a proton and form the alcohol again When water dissociates, the hydroxide ion only has one other hydrogen atom There is no extra electron density on the oxygen which is less likely to accept an H+ ion Page 125 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Water is therefore a stronger acid than alcohols Water is a stronger acid than alcohols as there are no electron-donating groups in the hydroxide ion, causing the O- to be less likely to accept a proton and reform water Page 126 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.5 Carbonyl Compounds 3.5.1 Production of Aldehydes & Ketones Production of Aldehydes & Ketones Aldehydes and ketones are carbonyl compounds containing a C=O group They can be prepared from the oxidation of primary and secondary alcohols respectively Oxidising agents The oxidising agents used to prepare aldehydes and ketones from alcohols include acidified potassium dichromate (K2Cr2O7) and acidified potassium manganate (KMnO4) Acidified with dilute sulfuric acid, potassium dichromate(VI), K2Cr2O7, is an orange oxidising agent When the alcohols are oxidised the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions Acidified with dilute sulfuric acid, potassium manganate(VII), KMnO4 is a purple oxidising agent When the alcohols are oxidised the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions Page 127 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The oxidising agents change colour when they oxidise an alcohol and get reduced themselves Synthesis of aldehydes To make an aldehyde, warm primary alcohol is slowly added to the oxidising agent The formed aldehyde has a lower boiling point than the alcohol and can therefore be distilled off as soon as it forms The aldehyde is then condensed into a liquid and collected Page 128 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Aldehydes are formed from the oxidation of primary alcohols Synthesis of ketones To make a ketone, warm secondary alcohol is slowly added to the oxidising agent Since the formed ketone cannot be further oxidised it does not need to be distilled off straightaway after it has been formed Page 129 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Ketones are formed from the oxidation of secondary alcohols Tip Exam If the aldehyde formed is not distilled off, further refluxing with excess oxidising agent will oxidise the aldehyde to a carboxylic acid. Page 130 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.5.2 Reactions of Aldehydes & Ketones Reactions of Aldehydes & Ketones Reduction of aldehyde & ketones Aldehydes and ketones can be reduced by reducing agents such as NaBH4 or LiAlH4 Aldehydes are reduced to primary alcohols Ketones are reduced to secondary alcohols Reduction of aldehydes and ketones to form primary and secondary alcohols Nucleophilic addition with HCN Aldehydes and ketones can undergo nucleophilic addition with hydrogen cyanide, HCN The cyanide ion, CN-, acts as a nucleophile and adds across the C-O bond Aldehydes and ketones react with HCN, KCN as catalyst and heat to produce hydroxynitriles Hydroxynitriles are nitriles containing a hydroxy, -OH, group Page 131 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Nucleophilic addition to ethanal (aldehyde) and propanone (ketone) Tip Exam The nucleophilic addition of HCN to an aldehyde or ketone increases the length of the carbon chain by one carbon atom! Page 132 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.5.3 Reaction with HCN Reaction of Hydrogen Cyanide with Aldehydes & Ketones The carbonyl group -C=O, in aldehydes and ketones is polarised The oxygen atom is more electronegative than carbon drawing electron density towards itself This leaves the carbon atom slightly positively charged and the oxygen atom slightly negatively charged The carbonyl carbon is therefore susceptible to attack by a nucleophile, such as the cyanide ion Nucleophilic addition The nucleophilic addition of hydrogen cyanide to carbonyl compounds is a two-step process In step 1 the cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate In step 2 the negatively charged oxygen atom in the reactive intermediate quickly reacts with aqueous H+ (either from HCN, water or dilute acid) to form 2-hydroxynitrile The cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate which quickly reacts with a proton to form a 2-hydroxynitrile compound Page 133 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Tip Exam The actual negative charge on the cyanide ion is on the carbon atom and not on the nitrogen atom. Page 134 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.5.4 Carbonyl Compound Tests Testing for Carbonyls: 2,4-DNPH 2,4-dinitrophenylhydrazine (also known as 2,4-DNPH) is a reagent which detects the presence of carbonyl compounds (compounds with -C=O group) The carbonyl group of aldehydes and ketones undergoes a condensation reaction with 2,4-dinitrophenylhydrazine A condensation reaction is a reaction in which two molecules join together and a small molecule (such as H2O or HCl) is eliminated The product formed when 2,4-DNPH is added to a solution that contains an aldehyde or ketone is a deep-orange precipitate which can be purified by recrystallisation The melting point of the formed precipitate can then be measured and compared to literature values to find out which specific aldehyde or ketone had reacted with 2,4-DNPH Ketones and aldehydes react with 2,4-DNPH in a condensation reaction The test tube on the left shows a negative 2,4-DNPH test and the tube on the right shows a positive test Page 135 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Tip Exam The 2,4-DNPH is especially useful as other carbonyl compounds such as carboxylic acids and esters do not give a positive test. Page 136 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Identifying Carbonyls: Fehling's Solution & Tollens' Reagent YOUR NOTES The presence of an aldehyde group (-CHO) in an unknown compound can be determined by the oxidising agents Fehling’s and Tollens’ reagents Fehling’s solution Fehling’s solution is an alkaline solution containing copper(II) ions which act as the oxidising agent When warmed with an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Cu2+ ions are reduced to Cu+ ions In the alkaline conditions, the carboxylic acid formed will be neutralised to a carboxylate ion (the -COOH will lose a proton to become -COO- ) The carboxylate ion (-COO-) will form a salt with a positively charged metal ion such as sodium (-COO-Na+) The clear blue solution turns opaque due to the formation of a red precipitate, copper(I) oxide Ketones cannot be oxidised and therefore give a negative test when warmed with Fehling’s solution The copper(II) ions in Fehling’s solution are oxidising agents, oxidising the aldehyde to a carboxylic acid and getting reduced themselves to copper(I) ions in the Cu2O precipitate Tollens’ reagent Tollens' reagent is an aqueous alkaline solution of silver nitrate in excess ammonia solution Tollens' reagent is also called ammoniacal silver nitrate solution When warmed with an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Ag+ ions are reduced to Ag atoms In the alkaline conditions, the carboxylic acid will become a carboxylate ion and form a salt The Ag atoms form a silver ‘mirror’ on the inside of the tube Ketones cannot be oxidised and therefore give a negative test when warmed with Tollens’ reagent Page 137 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The Ag+ ions in Tollens’ reagent are oxidising agents, oxidising the aldehyde to a carboxylic acid and getting reduced themselves to silver atoms Page 138 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.5.5 Iodoform Reaction Iodoform Reaction Tri-iodomethane (also called iodoform) forms a yellow precipitate with methyl ketones Methyl ketones are compounds that have a CH3CO-group Ethanal also contains a CH3CO- group and therefore also forms a yellow precipitate with iodoform The reagent is heated with an alkaline solution of iodine This reaction involves a halogenation and hydrolysis step In the halogenation step, all three H-atoms in the -CH3 (methyl) group are replaced with iodine atoms, forming a -CI3 group The intermediate compound is hydrolysed by an alkaline solution to form a sodium salt (RCO2- Na+) and a yellow precipitate of CHI3 The reaction of ethanal with iodoform results in the formation of a yellow CHI3 precipitate Page 139 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.6 Carboxylic Acids & Derivatives 3.6.1 Carboxylic Acids Production of Carboxylic Acids Carboxylic acids are compounds with a -COOH functional group They can be prepared by a series of different reactions Oxidation of primary alcohols & aldehydes Carboxylic acids can be formed from the oxidation of primary alcohols and aldehydes by either acidified K2Cr2O7 or acidified KMnO4 and reflux The oxidising agents themselves get reduced causing the solutions to change colour In K2Cr2O7 the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions In KMnO4 the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions Oxidation of primary alcohols (1) and aldehydes (2) gives carboxylic acids Hydrolysis of nitriles Carboxylic acids can also be prepared from the hydrolysis of nitriles using either dilute acid or dilute alkali followed by acidification Hydrolysis by dilute acid results in the formation of a carboxylic acid and ammonium salt Hydrolysis by dilute alkali results in the formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid The -CN group at the end of the hydrocarbon chain is converted to a -COOH group Page 140 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Hydrolysis of nitriles by either dilute acid (1) or dilute alkali and acidification (2) will form a carboxylic acid Hydrolysis of esters Esters are formed from the condensation reaction between an alcohol and carboxylic acid Hydrolysis of esters by dilute acid or dilute alkali and heat followed by acidification will reform the alcohol and carboxylic acid Hydrolysis by dilute acid, is a reversible reaction and an equilibrium is established Hydrolysis by dilute alkali is an irreversible reaction as all the ester is broken down to form a sodium carboxylate salt and an alcohol; acidification is required to change the carboxylate ion into a carboxylic acid Page 141 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Hydrolysis of esters by either dilute acid (1) or dilute alkali and heat followed acidification (2) will form a carboxylic acid Page 142 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Reactions of Carboxylic Acids YOUR NOTES Carboxylic acids are weak acids as they do not completely dissociate in water This means that the position of the equilibrium lies to the left and that the concentration of H+ is much smaller than the concentration of the carboxylic acid The solution has a pH value of less than 7 Carboxylic acids are weak acids that do not fully dissociate in water, the position of the equilibrium lies to the left Carboxylic acids are reactive compounds which can undergo many types of reactions including: Redox reactions with reactive metals Neutralisation reactions with alkali Acid-base reactions with carbonates Esterification with alcohols Reduction by LiAlH4 Page 143 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Carboxylic acids undergo a wide variety of reactions Page 144 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.6.2 Esters Production of Esters Esters are compounds with an -COOR functional group and are characterised by their sweet and fruity smells They are prepared from the condensation reaction between a carboxylic acid and alcohol with concentrated H2SO4 as catalyst This is also called esterification The first part of the ester’s name comes from the alcohol and the second part of the name comes from the carboxylic acid E.g. Propanol and ethanoic acid will give the ester propyl ethanoate Esters are formed from the condensation reaction between carboxylic acids and alcohols Page 145 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Hydrolysis of Esters YOUR NOTES Esters can be hydrolysed to reform the carboxylic acid and alcohol by either dilute acid or dilute alkali and heat When an ester is heated under reflux with dilute acid (eg. sulfuric acid) an equilibrium mixture is established as the reaction is reversible Ester hydrolysis by dilute acid is a reversible reaction forming carboxylic acid and alcohol However, heating the ester under reflux with dilute alkali (eg. sodium hydroxide) is an irreversible reaction as the ester is fully hydrolysed This results in the formation of a sodium carboxylate salt which needs further acidification to turn into a carboxylic acid The sodium carboxylate (-COO-) ion needs to get protonated by an acid (such as HCl) to form the carboxylic acid (-COOH) Ester hydrolysis by dilute alkali is an irreversible reaction forming a sodium carboxylate salt and alcohol Page 146 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.7 Nitrogen Compounds 3.7.1 Primary Amines Production of Amines Amines are compounds with the amine (-NH2) functional group They can be produced as a result of nucleophilic substitution reactions of halogenoalkanes when they are heated under pressure with ethanolic ammonia (NH3 in ethanol) The halogen atom in halogenoalkanes is more electronegative than the carbon atom it is bonded to The halogen, therefore, draws electron density from the C-X bond (where X is the halogen) towards itself The carbon, therefore, has a partial positive charge and the halogen itself has a partial negative charge The lone pair of electrons on the nitrogen atom (in NH3) acts as a nucleophile and attacks the partial positively charged carbon As a result of this nucleophilic attack, the C-X bond is broken and the halogen is substituted by an amine group Amine replaces the halogen in halogenoalkanes in a nucleophilic substitution reaction Page 147 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.7.2 Nitriles & Hydroxynitriles Production of Nitriles Nitriles are compounds with a -CN functional group They can be prepared from the nucleophilic substitution of halogenoalkanes Propanenitrile, an example of a nitrile Reaction with KCN The nucleophile in this reaction is the cyanide, CN- ion Ethanolic solution of potassium cyanide (KCN in ethanol) is heated under reflux with the halogenoalkane The product is a nitrile If an aqueous solution of potassium cyanide (KCN (aq)) is heated under reflux with the halogenoalkane, an alcohol can be formed instead of the nitrile Bromoethane reacts with ethanolic potassium cyanide when heated under reflux to form propanenitrile Tip Exam The nucleophilic substitution of halogenoalkanes with KCN adds an extra carbon atom to the carbon chain.This reaction can therefore be used by chemists to make a compound with one more carbon atom than the best available organic starting material. Page 148 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Production of Hydroxynitriles YOUR NOTES Hydroxynitriles are compounds with both a hydroxy (-OH) and cyanide (-CN) functional group They can be prepared from the nucleophilic addition of aldehydes and ketones 2-hydroxy-2-methylpropanenitrile Reaction with HCN The nucleophilic addition of hydrogen cyanide to carbonyl compounds is a two-step process In step 1, the cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate In step 2, the negatively charged oxygen atom in the reactive intermediate quickly reacts with aqueous H+ (either from HCN, water or dilute acid) to form a 2-hydroxynitrile Page 149 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources The cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate which quickly reacts with a proton to form a 2-hydroxynitrile compound Tip Exam The actual negative charge on the cyanide ion is on the carbon atom and not on the nitrogen atom. Page 150 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Hydrolysis of Nitriles Nitriles are hydrolysed by either dilute acid or dilute alkali followed by acidification to give a carboxylic acid Hydrolysis is the breakdown of a compound using water Hydrolysis of nitriles Nitriles are hydrolysed by either dilute acid or dilute alkali followed by acidification Hydrolysis by dilute acid results in the formation of a carboxylic acid and ammonium salt Hydrolysis by dilute alkali results in the formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid The -CN group at the end of the hydrocarbon chain is converted to a -COOH group Hydrolysis of nitriles by either dilute acid (1) or dilute alkali and acidification (2) will form a carboxylic acid Page 151 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources Tip Exam Unlike the formation of nitriles which add an extra carbon atom to the carbon chain, hydrolysis doesn’t change the number of carbon atoms. Page 152 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.8 Polymerisation 3.8.1 Addition Polymerisation Addition Polymerisation: Polythene & PVC Addition polymerisation Addition polymerisation is one of the most important addition reactions of alkenes which form the basis of the plastic industry Addition polymerisation is the reaction in which many monomers containing at least one CC double bond form long chains of polymers as the only product Just like in other addition reactions of alkenes, the π-bond in each C-C bond breaks and then the monomers link together to form new C-C single bonds A polymer is a long-chain molecule that is made up of many repeating units The small, reactive molecules that react together to form the polymer are called monomers A polymerisation reaction can be represented by a general formula or by using displayed formulae Eg. poly(ethene) and poly(chloroethene) (also known as PVC) are polymers made up of the ethene and chloroethene monomers respectively and are commonly used in making plastics The general formulae of the addition polymerisation of ethene (1) and chloroethene (2) Page 153 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The general formulae of the addition polymerisation of ethene (1) and chloroethene (2) Just like any other addition reaction of alkenes, addition polymerisation gives only one product Deducing repeat units A repeat unit is the smallest group of atoms that when connected one after the other make up the polymer chain It is represented by square brackets in the displayed and general formula In poly(alkenes) (such as poly(ethene)) and substituted poly(alkenes) (such as PVC) made of one type of monomer the repeating unit is the same as the monomer except that the C-C double bond is changed to a C-C single bond Page 154 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES The repeating units of poly(ethene) and poly(chloroethene) are similar to their monomer except that the C=C bond has changed into a C-C bond Worked example: Identifying monomers Page 155 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Answer 1: When ethenol (CH(OH)=CH2) is polymerised, the C-C double bond opens to produce a repeating unit of CH(OH)-CH2. This gives the polymer poly(ethenol) Answer 2: Page 156 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources To find the monomer, first the repeating unit should be deduced. Repeating units have only 2 carbons in the polymer main chain Since the repeating unit is now found, it can be concluded that the monomer is prop-2enoic acid Answer 3: Again, the repeating unit only has 2 carbons in the polymer chain which in this case are two carbon atoms that each contain one OH group Thus, when ethene-1,2-diol (CH(OH)=CH(OH)) is polymerised, the C-C double bond opens to produce a repeating unit of CH(OH)-CH(OH) which gives the polymer poly(ethene-1,2-diol) Page 157 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers YOUR NOTES Head to savemyexams.co.uk for more awesome resources YOUR NOTES Tip Exam The section of the polymer chain shown inside the square brackets by the structural or displayed formula is the repeat unit and not the monomerThe monomer is the same as the repeat unit except for that it has C=C bonds instead of C-C bonds Page 158 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.8.2 Disposal of Polymers Disposal of Polymers Though poly(alkenes)s are extremely important in everyday such as their use as plastics, the disposal of these polymers is problematic Poly(alkenes) are very large alkane molecules which are unreactive and therefore do not undergo any chemical reactions; they are resistant to chemical attack Due to their unreactivity, polymers are non-biodegradable and take up to hundreds of years to decompose when dumped in landfill sites Throwing away poly(alkenes) therefore cause the long-term pollution of the environment Burning the polymers results in harmful combustion products which again cause the pollution of the environment Tip Exam The disposal of polymers is a challenge due to their unreactivity, their non- biodegradability, and the formation of harmful combustion products when burnt. Page 159 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.9 Organic Synthesis 3.9.1 Organic Synthesis Elucidating Organic Molecules You are expected to be able to identify organic functional groups, their properties, how to test for their presence and how they are made Functional groups The table below summarises the tests to identify the presence of certain functional groups and the reactions to make them Functional groups, their reactions & identifying tests table Page 160 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 161 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 162 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 163 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Types of reactions You should also be aware of the different type of reactions that functional groups can undergo Reactions of functional groups table Page 164 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Oxidising & reducing agents Certain functional groups only react with specific oxidising and reducing agents which you should be aware of Oxidising & reducing agents table Page 165 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 166 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Tests The test also requires you to distinguish between the different tests that identify functional groups in a compound Tests identifying functional groups in a compound table Worked example: Elucidating organic molecules Page 167 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 168 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 169 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 170 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.9.2 Multi-Step Synthesis Multi-step Synthetic Routes Many organic molecules are made in multi-step synthetic routes Students should be able to recall the different reactions each functional group undergoes and apply this knowledge when devising multi-step synthetic routes for preparing organic molecules Worked Example: Devising a multi-step synthesis Page 171 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 172 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 173 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Page 174 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES 3.9.3 Synthetic Routes Analysis of Synthetic Routes Students should be able to critically analyse given synthetic routes and determine whether appropriate reagents and reaction conditions are used Students should also be able to predict possible by-product of a synthetic reaction Worked Example: Two-step synthesis Answer The correct answer is D The first step involves a nucleophilic addition of CN- using NaCN as catalyst and heat to form a hydroxynitrile. In the second step, the nitrile is refluxed with dilute aqueous sulfuric acid causing hydrolysis of the nitrile forming a carboxylic acid and ammonium salt. Worked Example: Synthesis of hexanoic acid Page 175 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources YOUR NOTES Answer The correct answer is C Halogenoalkanes can undergo nucleophilic substitution with ethanolic KCN in which the CN- ion acts as a nucleophile and replaces the chlorine atom in 1-chloropentane to form a nitrile. The treatment of nitriles with concentrated hydrochloric acid will produce a carboxylic acid and an ammonium salt. In this case, hexanoic acid and ammonium chloride will be formed. Page 176 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to savemyexams.co.uk for more awesome resources Page 177 of 177 © 2015-2023 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers
