Chemistry 29: Classes of Organic Compounds

1. Chemistry 29: Classes of Organic Compounds Christopher Chui Classes of Organic Compounds - C. Chui

2. Classification of Hydrocarbons • Hydrocarbons contain hydrogen and carbon atoms • Hydrocarbons are classified as aromatic or aliphatic • Alkane is a chain compound with single bond C-C • A saturated H-C is an alkane with single bond C-C • Each alkane differs from the next by –CH2– group • Alkanes are also called the paraffin series • Each member of a homologous series differs from each other member by a specific structural unit • The general formula for alkanes: CnH2n+2 • CH4 methane, C2H6 ethane, C3H8 propane • A HC radical is a HC molecule from which a H atom removed • Radicals are named by substituting the –yl from the -ane Classes of Organic Compounds - C. Chui

3. Naming Branched Alkanes • CH3- methyl, C2H5- ethyl, C3H7- propyl, C4H9- butyl, C5H11- pentyl, C6H13- hexyl, C7H15- heptyl, C8H17- octyl, C9H19- nonyl, C10H21- decyl • Carbon atoms in a structural formula are given position numbers, 1, 2, 3, 4, etc • Alkanes are named on the basis of the longest continuous chain of carbon atoms (parent chain) • Parent chain does not need to be straight • Substituents or branch chains are attached to the main chain of carbon atoms • Carbons are numbered so as to give the lowest position numbers to the branches Classes of Organic Compounds - C. Chui

4. Alkane’s Isomers & Cycloalkanes • Isomers have the same formula but different molecular structures • Butane and 2-methylpropane are isomers • Pentane, 2-methybutane, and 2,2-dimethylpropane • Cycloalkanes are single-bond ring compounds with the general formula CnH2n • A strained bond results when the molecular geometry shows the bonding electrons to be closer than the normal 109.5 degrees Classes of Organic Compounds - C. Chui

5. Alkenes and its Naming • Alkenes are unsaturated hydrocarbon that contain double bonds • General formula for alkenes: CnH2n • A double bond is stronger than a single bond • Alkene isomers differ in the location of their double bonds • Compounds are named according to the longest chain that includes a double bond • Number the chain so the lowest possible position number is assigned to the first double-bonded carbon atom • Geometric isomerism may result from double bonds • Double bonds are also found in cyclic compounds • A molecule whose name ends in –diene contains 2 double bonds Classes of Organic Compounds - C. Chui

6. Alkynes & Aromatic Hydrocarbons • Alkynes contain triple bonds and have the general formula CnH 2n+2 • Alkynes are very reactive • Number the chain so the lowest possible number is assigned to the first triple-bonded carbon atom • The benzene ring contains a conjugated system of bonds • Aromatic compounds are generally derived from benzene • Naphthalene, C10H8, has a fused ring structure • The phenyl radical is formed by removing a hydrogen atom from a benzene • Aromatic compounds are economically important to many chemical industries such as rubber, plastics, fibers, explosives, paint, and petroleum Classes of Organic Compounds - C. Chui

7. Halogen Derivatives • Substitutions in a hydrocarbon generally increase the reactivity • A halogen derivative has a halogen atom substituted for a hydrogen atom • Substituted hydrocarbons are named with the lowest possible position numbers for substituents • Note that the double bond has precedence over the halogen when numbering the parent chain • The halogen-substituted hydrocarbon ethyl chloride is often used as a local anesthetic. Iodoform is used as an antiseptic Classes of Organic Compounds - C. Chui

8. Organic Oxygen Compounds • Class: alcohol, formula R—O—H, ending –ol • Class: ether, formula R—O—R’, ending –oxy- • Class: aldehyde, formula R—CO—H, ending –al • Class: ketone, formula R—CO—R’, ending –one • Class: acid, formula R—CO—O—H, -oic acid • Class: ester, formula R—CO—O—R’, -yl –oate • Alcohols contain the hydroxyl group, --OH • Phenol is formed when a hydroxyl group attaches to a benzene ring • Cranberries—benzoic acid, grapes—tartaric acid, citrus fruits—citric acid, sour milk—lactic acid, rhubarb—oxalic acid, green apples—malic acid Classes of Organic Compounds - C. Chui

9. Organic Acids • Organic acids contain the carboxylic acid group R—COOH • Many esters have pleasant odors: ethyl butyrate—pineapple, ethyl formate—rum, methyl butyrate—apple, methyl salicylate—wintergreen, octyl acetate—orange, pentyl acetate—banana, pentyl butyrate—apricot • Hexanedioic acid (adipic acid) is synthesized from cyclohexane in making nylon • Vinyle acetate is an ester produced from ethyne and ethanoic acid to make adhesives and paints Classes of Organic Compounds - C. Chui

10. Organic Nitrogen Compounds • An amine contains nitrogen bonded to alkyl groups and hydrogen atoms • Amines are Lewis bases since the N atom has an unshared pair of electrons • 3 amines have bad odors: putrescine C4H12N2, and cadaverine, C5H14N2bad breath, trimethylamine, C3H9Nrotting fish odor • Amides are characterized by a carbonyl group and an amine group • Nitriles contain a carbon-nitrogen triple bond Classes of Organic Compounds - C. Chui

11. Organic Compounds with Nitrogen • Class: amines, formula R—NH2, ethanamine • Class: amides, formula R—CO—NH2, ethanamide • Class: amino acids, formula G—CHNH2—COOH, alanine (2-aminopropanoic acid) • Class: nitriles, formula R—CN, butanenitrile • Class: nitro compounds, formula R—NO2, nitrobenzene • One important nitrile is propenenitrile, manufactured from propene, ammonia, and oxygen to make fibers, plastics, and synthetic rubber Classes of Organic Compounds - C. Chui