CHEMISTRY 122 HW CH#4 AROMATIC COMPOUNDS 4, 6, 8, 10, 14, 16, 18, 20, 22, 24, 26, 38, 40 4-4 An aromatic compound is one that contains one or more benzene rings. 4-6 Aromatic rings have double bonds in the contributing structures we normally use to represent them. They are unsaturated because they have fewer hydrogen atoms than a cycloalkane with the same number of carbons. 4-8 (a) An alkene of six carbons has the molecular formula C6H12 and contains one carbon-carbon double bond. Three examples are: 1-Hexene trans-3-Hexene cis-3-Hexene (b) A cycloalkene of six carbons has the molecular formula C6H10 and contains one ring and one carbon-carbon double bond. Three examples are: Cyclohexene 4-Methylcyclopentene 1-Methylcyclopentene (c) An alkyne of six carbons has the molecular formula C6H10 and contains one carbon-carbon triple bond. Three examples are: 1-Hexyne 2-Hexyne 4-Methyl-2-pentyne (d) An aromatic hydrocarbon of eight carbons has the molecular formula C8H10 and contains one benzene ring. Three examples are: Ethylbenzene 1,3-Dimethylbenzene (m-Xylene) 1,4-Dimethylbenzene (p-Xylene) 4-10 Benzene consists of carbons, each surrounded by three regions of electron density, which gives 120° for all bond angles. Bond angles of 120° in benzene can be maintained only if the molecule is planar. Cyclohexane, on the other hand, consists of carbons, each surrounded by four regions of electron density, which gives 109.5° for all bond angles. Angles of 109.5° in cyclohexane can be maintained only if the molecule is nonplanar. 4-14 (a) (b) (c) (d) (e) (f) (g) (h) 1-Chloro-4-nitrobenzene (p-chloronitrobenzene) 2-Bromotoluene (o-bromotoluene) 1-Chloro-3-phenylpropane 2-Bromo-2-phenylbutane 2-Nitroaniline (o-nitroaniline) 2-Phenylphenol (o-phenylphenol) trans-1,2-Diphenylethene (trans-1,2-diphenylethylene) 2,4-Dichlorotoluene 4-16 Polynuclear means that each contains two or more rings bonded in such a way that each ring shares two adjacent atoms with another ring. Aromatic means that each ring is six-membered and has three carbon-carbon double bonds; that is, each has an aromatic sextet. Hydrocarbon means that these compounds consist of only carbon and hydrogen. 4-18 (a), (b), (c), (d): True 4-20 Br Br Br Cl 13.20 Cl 1-Bromo-2chlorobenzene (o-Chlorobromobenzene) 1-Bromo-3chlorobenzene (m-Chlorobromobenzene) Cl 1-Bromo-4chlorobenzene (p-Chlorobromobenzene) 4-22 (a) Nitration using HNO3/H2SO4 (b) Bromination using Br2/FeCl3 (c) Nitration using HNO3/H2SO4 followed by catalytic reduction using H2/Ni 4-24 The two sulfonated naphthalenes are: SO3H SO3H 1-Naphthalenesulfonic acid 2-Naphthalenesulfonic acid 4-26 Phenol is a sufficiently strong acid that it reacts with strong bases such as sodium hydroxide to form sodium phenoxide, a water-soluble salt. Cyclohexanol has no comparable acidity and does not react with sodium hydroxide 4-38 A substance that is biodegradable can chemically breakdown into environmentally friendly products, usually by bacteria or other biological means. 4-40 Iodine is an element that is found primarily in seawater and, therefore, seafood is a rich source of it. Individuals in inland areas where seafood is only a limited part of the diet are the most susceptible to developing goiter.