CHAPTER 11 BONDING AND MOLECULAR STRUCTURE: ORGANIC CHEMISTRY All bold numbered problems. Overview • Organic chemistry is the study of compounds containing carbon combined with other non-metals. • Bonding plays a critical role in understanding the reactivity of these compounds. • These compounds are referred to as hydrocarbons since they are primarily hydrogen and carbon. Overview Overview • Carbon uses sp3, sp2, and sp hybridization in forming the four bonds per carbon atom common to almost all carbon compounds. • With sp hybridization, there are two (2) p bonds and 2 s bonds. • With sp2 hybridization there is one (1) p bond and 3 s bonds. Why Carbon sp3, sp2, and sp hybridization Allotropes of Carbon Carbon only (no other atom) compounds importance FUNCTIONAL GROUPS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Alkane Organic chemistry is the study of Alkene compounds containing carbon. Alkyne The goal of studying Organic Alkyl halide chemistry is the making of carbon-carbon bonds, C-X, C-O, C-N, Aromatic and C-S bonds to make new molecules Alcohol Aldehyde Ketone Carboxylic Acid Ester Inorganic molecules like CO, and Amine CO3-2 are not considered organic Amide molecules. 1. Alkanes Figure 11.4 10 Structural Formula BP (C) MP (C) 1 CH4 -161 -183 ethane 2 CH3CH3 -88 -172 propane 3 CH3CH2CH3 -45 -187 butane 4 CH3CH2CH2CH3 -.5 -138 pentane 5 CH3CH2CH2CH2CH3 36 -130 hexane 6 CH3CH2CH2CH2CH2CH3 69 -95 heptane 7 CH3CH2CH2CH2CH2CH2CH3 98 -90 octane 8 CH3CH2CH2CH2CH2CH2CH2CH3 125 -57 nonane 9 CH3CH2CH2CH2CH2CH2CH2CH2CH3 151 -54 decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH 175 -30 Name # of C's methane 3 Alkanes 12 Abbreviated, common method to write organic cmpds Name methane Structural Formula C CH4 ethane CH3CH3 propane CH3CH2CH3 butane CH3CH2CH2CH3 pentane CH3CH2CH2CH2CH3 ALKANES • There are frequently many hydrocarbons with the same formula. These are called structural isomers. C5H12 has three isomers C10H22 has 75 isomers C20H42 has 366,319 isomers Isomers of Butane-5 Carbon chains C6H14 has five isomers, draw them. Cycloalkanes • Cycloalkanes are ring structures and have the general formula CnH2n. • Do not confuse these compounds with the alkenes which have the same general formula. 2. ALKENE AND 3. ALKYNE • These compounds are referred to as unsaturated. • Alkenes contain one or more double bonds and alkynes contain one or more triple bonds. Saturated –vs- Unsaturated Saturated Hydrocarbon C15H32 Unsaturated Hydrocarbon Contains either double and/or triple bonds Notice how the chains do not line up ALKENES ALKYNE Physical properties change Isomers have different physical as well as different chemical properties Nomenclature • Organic Functional Groups and Nomenclature • Substituents - saturated carbon substituents are called alkyl groups and are named based on the naming of the normal alkanes. H methy l C H H CH3 Me H e t hyl H H H C C H H H CH2C H3 Et Nomenclature Haloalkane 26 Alcohol 27 Ether 28 Amine 29 Aldehyde 30 Ketone 31 Carboxylic acid 32 Ester 33 Amide Common Alcohol Names What is the name of this Alcohol? alcohol methyl Methanol The main chain is numbered such that the first substituent encountered along the chain receives the lowest possible number. CH 3 C 1 C 2 C 3 C 4 C 5 2-methylpentane CH 3 C 5 C 4 NOT C 3 4 -m ethylpent ane C 2 C 1 If two or more identical substituents are attached to the same C-chain , prefixes di-, tri-, tetra-, etc. are used with numbers to indicate position. CH 3 C 1 C 2 CH3 C 3 C 4 C 5 2 ,4- dimethylpent ane CH3 C 1 2 C C 3 C 4 C 5 CH3 2, 2-dimethylpentane If two different substituents are attached to the carbon chain, name them in alphabetical order. CH CH 2 C 1 C 2 CH 3 C 3 3 C 4 C 5 Numbering starts at the side with the heavier functional Group 2- ethyl-4-methylpentane CH 3 C 1 C 2 CH2CH3 C 3 C 4 Numbering starts closest 4-ethyl-2-methylhexane to 1st functional group C 5 C 6 Practice C C C C C C C C C 3 C C 2 C 4 C 5 C 6 C 1 3-ethylhexane C Practice methylcyclopentane 1-ethyl-2-methylcyclopentane Practice Br C C Cl C C C 2-bromo-4-chloropropane Br C C Br C C Br 2,2,4-tribromopropane C Draw the following • • • • • • Butane Butene Butyne Butanol Butanal Butanone • • • • • • Dibutyl ether Butanoic acid Butyl butanoate Butyl amine Dibutyl amine Tributyl amine Structure, Bonding, and Isomerism • Alkenes have the possibility of cis- transisomerism since the pi bond does not permit rotation. • Illustration: the three isomers of butene (isobutene is actually a propene). • The position of the atoms changes the physical properties listed. • If a molecule has two double bonds between carbon atoms, it is called a diene. Double and Triple Bonds Double and Triple Bonds trans-2-butene Double and Triple Bonds trans-2-pentene 1. Draw a cis, trans-2,4-heptene 2. Name the following Preparation of Alkenes and Alkynes • Acetylene aka ethyne, from calcium carbide, CaC2 • Steam cracking for the formation of ethylene, ethene, from ethane. Addition Reactions • Symmetrical addition is simple, but asymmetrical addition follows Markovnikov's rule: the hydrogen adds to the carbon with the most hydrogen. For alkynes, the addition is always two mole to one mole of alkyne, the product being a substituted alkane. If hydrogen gas is added, the process is called hydrogenation. Markovnikov Addition Br CH3CH2CH2CH2CH2 C CH HBr ethanol ? CH3CH2CH2CH2CH2 C H HBr CH ethanol Br ? CH3 CH2CH2CH2CH2 C Br H CH H The hydrogen adds to the carbon with the most hydrogen ALKENE to ALKANE ALKENES: Addition ALKENES: Elimination AROMATIC COMPOUNDS Naphthalene Benzene AROMATIC COMPOUND • See your text for physical properties of these compounds. • Aromatics like benzene have sp2 hybridization with delocalized pi electrons. The delocalized p bonding is the key to these compounds. • They do not undergo addition reactions like alkenes and alkynes, but rather react by way of substitution. Substitution reactions with aromatic compounds, not addition CnH2n+2 CnH2n CH3 CH2 CH3 CH2 + Br2 + Br2 no react ion H Br Br C C H H H Br CnHn + Br2 + HBr Naming Aromatic Compounds OH CH3 CH3 CH3 phenol toluene napthalene o-xylene anthracene X ortho -- o meta -- m para -- p CH3 CH3 CH3 CH3 p-xylene o-xylene CH3 m-xylene CH3 Benzene Reactions halogenation Br + Br2 + HBr Benzene Reactions nitration NO2 + HNO3 (conc) H2SO4 (conc) + H3O+ Benzene Reactions alkylation CH2CH2CH2CH3 CH3CH2CH2CH2Cl AlCl3 ALCOHOLS ALCOHOLS Naming Alcohols • The alkane name is modified by dropping the e and adding ol. CH3CH2OH is ethanol • If three OH groups are present, the molecule is called a triol. CH3C(OH)3 is ethantriol Primary, secondary, and tertiary alcohols H C R R R OH H primary or 1° R C OH H secondary or 2° R C OH R tertiary or 3° What type of alcohol’s are these? 1°, 2°, 3°? Metalation of Alcohols Sodium metal reacts with an alcohol to produce hydrogen gas and the sodium alkoxide, refered to as a metalation, since the oxygen is still attached. CH3CH2OH + NaH OH CH3CH2O-Na+ + H2 O-Na+ + NaOH + H2O 67 Chemistry of Alcohols 1. Alcohols can go through substitution, and elimination reactions Which means Alcohols are either oxidized or reduced Formation of ALCOHOLS addition reaction to an alkene H2C CH2 + H2O H3PO4 CH3CH2OH Could also be called an oxidation reaction because we’re adding oxygen to the carbon Substitution • An alcohol reacts with HX to produce the alkylhalide and water, where X is Cl, Br, I • CH3CH2OH + HCl CH3CH2Cl + H2O Elimination • In the presence of concentrated sulfuric acid and heat an alcohol will eliminate water and form an alkene; the reverse of how alcohols are formed. 70 Addition to Ethylene or Elimination by ALCOHOLS H2C CH2 + H2O H3PO4 CH3CH2OH H2SO4 Forward is an oxidation, the reverse a reduction. Alcohols can be oxidized to carboxylic acids or ketones 1. primary alcohols to aldehydes with mild Oxidizing agents O PCC CH3CH2 PCC = C OH H3C N+ H CrO3Cl- Pryidinium chlorochromate H Alcohols can be oxidized directly to carboxylic acids or ketones 1. primary alcohols directly to acids by STRONG oxidizing agents O CH3CH2 OH CrO3, H+ C H3C OH Alcohols can be oxidized to carboxylic acids or ketones 2. secondary alcohols to ketones O OH PCC CH CH3 CH3 2-propanol C H3C CH3 propanone Tertiary alcohols No reaction OH PCC, or CrCl3 CH3 C CH3 no reaction CH3 Why? CARBONYLCOMPOUNDS The carbonyl group is a carbon atom double bonded to an oxygen atom, and is found in aldehydes, ketones, carboxylic acids, and esters. O C 76 Suggest a method for making CARBONYL COMPOUNDS CARBONYL COMPOUNDS • The aldehyde has at least one hydrogen atom bonded the carbonyl carbon. • The ketone has two carbon atoms bonded to the carbonyl carbon. • The carboxylic acid has an OH bonded to the carbonyl carbon. • The ester is a combination of an alcohol and a carboxylic acid. • aldehyde, RCOH; carboxylic acid, RCOOH; ketone, RCOR'; ester, RCOOR'. CARBONYL COMPOUNDS • Carboxylic acids can be formed by oxidizing primary alcohols or aldehydes. • Reducing aldehydes and acids with NaBH4 or LiAlH4 produces a primary alcohol. • Reduction of a ketone produces a secondary alcohol. 80 Esters • Form from carboxylic acids and alcohols when heated with sulfuric acid. They are named from the alcohol and the acid with an ate ending CH3CH2OH + CH3COOH CH3COOCH2CH3 81 Esters • In basic solution, esters are hydrolyzed to the alcohol and the salt of the carboxylic acids Alkyl halides RX • React to form alcohols in water using a strong base like NaOH, substitution reaction. • In an alcohol solvent, the same reactants form an alkene, elimination reaction. 83 Alkyl halides • RX react with magnesium metal to form a Grignard reagent. • This reagent reacts with aldehydes and ketones to form alcohols and with carbondioxide to form carboxylic acids. Ethers R-O-R’ (Additional material) • Ethers, R-O-R', can be formed from the reaction of alcohols when heated in the presence of concentrated sulfuric acid. • See Lab IVCX 15 11.6 FATS AND OILS • Fats and oils are esters of glycerol 1, 2, 3-propanetriol • The R group of the triester is a long chain fatty acid. BOOM! FATS AND OILS • Some fats are saturated, some unsaturated, and some are polyunsaturated. • When the triester is hydrolyzed with strong base, the sodium or potassium salt forms and is called a soap. –The process is also called saponfication. Single bonds only Fats Double bonds Fats AMINES AND AMIDES • React as bases and have bad smells • React with carboxylic acids to form amides which are similar in structure to esters. AMINES AMIDES Polymers S U L F U R 11.7 SYNTHETIC POLYMERS • Polymers are formed from combinations of monomers. • They can be classified many ways. –Thermoplastics can be heated and reformed again and again. –Thermosetting plastics are heated and formed, but cannot be heated and reformed because of their high degree of cross-linking. 11.7 SYNTHETIC POLYMERS • Another classification system for polymers is based on their intended use: - plastics - fibers - Elastomers - coatings - adhesives • Polymers can also be classified by the way they form: –addition polymers –condensation polymers Addition Polymers • The monomers for these polymers all have a double bond. • If an appropriate initiator is added, these monomers can add to the chain one at a time by breaking the double bond. • This process is called chain growth polymerization. • Copolymers are formed from a mixture of monomers. 97 Addition: Free Radical Polyethylene: Addition CH2 CH2 CH2 CH2 n Polypropylene CH3 CH CH3 CH2 CH CH2 n (a) Linear, straight Polyethylene Branching Bridging, crosslink Teflon CF2 CF2 CF2 CF2 n What would the following addition polymers look like O C O Cl CH CH2 for PVC CH2 CH3 CH methyl methacrylate for Lucite, Plexiglass CH CH2 stryene for styrofoam PETE (polyethylene terephthalate), HDPE (highdensity polyethylene), LDPE (low-density polyethylene), PP (polypropylene), CLPE (cross-linked polyethylene, V (vinyl) or PVC, also RLDPE (resin mix, already recycled. The # is another way of identifying that polymer. Condensation Polymers • These polymers are usually copolymers. • One monomer is a dicarboxylic acid and the other monomer is either a dialcohol or a diamine. • These polymers are named as polyesters or polyamides. Nylon 66 Polyamide Chains Monomers Polymer 107