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 C carbon-carbon double bond. Three examples are:
6
H
12
and contains one
1-Hexene trans3-Hexene cis -3-Hexene
(b) A cycloalkene of six carbons has the molecular formula C
6
H
10
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 C
6
H
10
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 C
8
H
10 and contains one benzene ring. Three examples are:
Ethylbenzene 1,3-Dimethylbenzene
( mXylene)
1,4-Dimethylbenzene
( pXylene)
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,

4-22
4-24 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
4-16
(a) 1-Chloro-4-nitrobenzene (
(b) 2-Bromotoluene (
(g)
(h) trans o
2,4-Dichlorotoluene p -chloronitrobenzene)
-bromotoluene)
(c) 1-Chloro-3-phenylpropane
(d) 2-Bromo-2-phenylbutane
(e) 2-Nitroaniline ( o -nitroaniline)
(f) 2-Phenylphenol ( o -phenylphenol)
-1,2-Diphenylethene ( trans -1,2-diphenylethylene)
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
4-20
(a), (b), (c), (d): True
Br Br Br
Cl
13.20
Cl
1-Bromo-2chlorobenzene
( oChlorobromobenzene)
1-Bromo-3chlorobenzene
( mChlorobromobenzene)
Cl
1-Bromo-4chlorobenzene
( pChlorobromobenzene)
(a) Nitration using HNO
3
/H
2
SO
4
(b) Bromination using Br
2
/FeCl
3
(c) Nitration using HNO
3
/H
2
SO
4
followed by catalytic reduction using H
2
/Ni
The two sulfonated naphthalenes are:

SO
3
H
SO
3
H
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.