What is Organic Chemistry?
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Organic Chemistry By Ryan Introduction to Organic Chemistry Watch the following FUN VIDEO! https://www.youtube.com/watch?v=UloIw7dhnlQ What is Organic Chemistry? - Simply defined, organic chemistry is a branch of chemistry related to the study of organic compounds - Organic compounds are usually carbon-containing compounds (Note: There may be exceptions to this definition where carbon-containing compounds such as carbonates are not classified as an organic compound) Homologous Series - Organic compounds can be divided into further subgroups. Each subgroup is known as a homologous series. - A homologous series is a family of compounds with the same general formula and similar chemical properties. Functional Groups - Except for alkanes, the compounds in each homologous series contain a group of atoms known as a functional group. - A functional group is a group of atoms that gives an organic compound its chemical properties and determines what kind of reactions organic compounds can undergo - Organic compounds in different homologous series have different functional groups Examples of homologous series Note: n refers to the number of carbon atoms in the organic compound and R refers to a carbon side-chain Homologous series General formula Functional group Example Alkanes CnH2n+2 C-C Methane Alkenes CnH2n C=C Ethane Aldehyde CnH2n+1CHO CHO Methanal Alcohol CnH2n+1OH OH Methanol CnH2n+1COOH COOH Ethanoic acid R-COO-R’’ COO Methyl ethanoate Carboxylic acids Ester Prefixes - Prefixes in the names of organic compounds show the number of carbon atoms in the organic compounds. Number of carbon atoms Prefix Number of carbon atoms Prefix 1 Meth- 6 Hex- 2 Eth- 7 Hept- 3 Prop- 8 Oct- 4 But- 9 Non- 5 Pent- 10 Dec- Examples Alkanes - General Formula CnH2n+2 Aldehydes - General Formula CnH2n+1CHO Number of carbon atoms Name/Molecular Formula Number of carbon atoms Name/ Molecular Formula 1 Methane (CH₄) 5 Pentanal (C₅H₁₁CHO) 2 Ethane (C₂H₆) 6 Hexanal (C₆H₁₃CHO) 3 Propane (C₃H₈) 7 Heptanal (C₇H₁₅CHO) 4 Butane (C₄H₁₀) 8 Octanal (C₈H₁₇CHO) Structure of organic compounds - An organic compound is said to be saturated if each carbon atom in the organic compound is bonded to the maximum number of other atoms (Each carbon atom can bond to a maximum of 4 other atoms as they are tetravalent) - Examples of saturated organic compounds are the alkanes and the cycloalkanes. Properties of Alkanes/Alkenes - Alkanes are unreactive as they are saturated - Alkenes are reactive as they are unsaturated (due to the presence of C=C bonds) - Boiling points and melting points of alkanes/alkenes increase as the number of carbon atoms increases due to an increase in the van der Waal’s forces of attraction (Methane is a gas, but octadecane is a solid) - Alkanes/Alkenes are insoluble in water but are soluble in organic solvents - Alkanes/Alkenes are less volatile as the number of carbon atoms increases due to an increase in the van der Waal’s forces of attraction - Alkane/Alkenes are denser as the number of carbon atoms increases Reaction of alkanes (1) - Combustion Alkanes/Alkenes burn in excess oxygen to form carbon dioxide and water. Incomplete combustion of alkanes/alkenes forms carbon monoxide and water. Example Methane + Oxygen _ CH₄ + _ O₂ Carbon Dioxide + Water _ CO₂ + _ H₂O Reaction of alkanes (2) - Substitution reaction (Only occurs for alkanes) A substitution reaction is a reaction in which an atom or group of atoms replace other atoms in a molecule Example - Chlorination of alkanes under UV light (free radical substitution) Methane + Chlorine Chloromethane + Chlorine Chloromethane + Hydrogen Chloride Dichloromethane + Hydrogen Chloride Note: Presence of UV light is a necessary condition for chlorination of alkanes Reaction of alkenes (1) - Addition reactions (Alkenes only) An addition reaction is a reaction in which two or more molecules combine to form a single product. Example 1 - Hydrogenation of alkenes to produce alkanes with nickel as a catalyst Example 2 - Bromination of alkenes to produce bromoalkanes Example 3 - Hydration (reaction with steam) of alkenes to produce alcohols Conditions needed for Example 3 : 300°C , 60-70 atm pressure, with phosphoric (V) acid as the catalyst Reaction of alkenes (2) - Polymerisation Polymerisation is a process whereby many identical alkene molecules join together in an addition reaction to form a big molecule known as a polymer. Example - Polymerisation of ethene to form poly(ethene) Testing for Unsaturated Compounds - Aqueous bromine can be used to test for unsaturated compounds - When unsaturated compounds are added into bromine, the solution changes from reddish-brown in colour to colourless (decolourisation) - This is because the unsaturated compounds undergo addition reactions with the aqueous bromine and are brominated Isomers - Isomers are different compounds with the same molecular formulae but different structural formulae and different boiling points. - There are many types of isomerism: cis-trans isomerism, functional group isomerism, optical isomerism, positional isomerism and chain isomerism - Example of isomers are the alkenes and cycloalkanes Cracking of petroleum fuel - Large alkane molecules in petroleum can be broken down into smaller molecules through cracking. - Two types: Catalytic cracking (passed over catalyst) and steam cracking (mixed with steam) - When an alkane is cracked, there are many different combination of products that can be formed. - For example, cracking of decane can produce propene + heptane OR propene + heptene + hydrogen - Cracking is mainly used to provide fuel for vehicles and produce hydrogen Properties of Alcohols/Carboxylic Acids - Alcohols/ Carboxylic acids have low boiling points and as the number of carbon atoms in the alcohols increase, the boiling points of the alcohols increase. - Alcohols are soluble in water. As the number of carbon atoms in the alcohols increase, their solubility in water decreases. - Carboxylic acids also have chemical properties similar to that of typical acids. Reactions of alcohols - Combustion to produce carbon dioxide and water - Oxidation to produce a carboxylic acid Example : Oxidation of ethanol to ethanoic acid with acidified potassium manganate (VII) solution - Esterification (Reaction with carboxylic acids to form esters) Esters - An ester is an organic compound formed due to the reaction between an alcohol and a carboxylic acid. - Carboxylic acid + Alcohol ester + water - Esters are sweet-smelling, good solvents for organic compounds and have low boiling points - Esters have the general formula of R-COO-R’’ where R and R’’ are carbon side chains Note: The sweet smell of fruits such as bananas can be attributed to esters! Nomenclature for Esters - Esters are named by placing the prefix of the alcohol reactant at the front and the prefix of the carboxylic acid reactant at the back - Example: Methanol + Ethanoic acid Methyl ethanoate + Water THE END THANK YOU AND HOPE YOU HAD FUN !!!
