Chapter 12.5
Aromatic Hydrocarbons
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Aromatic Compounds and
Benzene
• Aromatic compounds contain benzene.
• Benzene, C6H6 , is represented as a six
carbon ring with 3 double bonds.
• Two possible isomers can be drawn to show
benzene in this form.
H
H
H
H
H
H
H
H
H
H
H
H
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Aromatic Compounds and
Benzene
• The name aromatic came from many of the first
examples discovered were pleasant smelling
• Many aromatics that have recently been
discovered are not pleasant smelling, though
• The most common aromatic ring is benzene
which includes 6 Carbons and 6 Hydrogens--it
is highly unsaturated
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Aromatic Compounds and
Benzene
• Strangely, aromatics do not undergo the same kinds
of reactions as alkenes and alkynes
• The benzene ring is planar and hexagonal
• The three double bonds in benzene are shared
equally between the six carbons. We say that the
double bonds are delocalized
• Benzene is unusually stable and resists most
reactants
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Benzene Structure
The structures for benzene can also be
written as a single structure where the
alternating double bonds are written as a
circle within the ring.
Benzene
structure
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Aromatic Compounds in Nature
and Health
Many aromatic compounds are common in nature
and in medicine.
CHO
COOH
COOCH3
CH3
CH3
CH3CHCH2
CHCOOH
OCH3
OH
Aspirin
Vanillin
Ibuprofen
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Naming Aromatic Compounds
Aromatic compounds are named with
benzene as the parent chain. One side group
is named in front of the name benzene.
CH3
methylbenzene
(toluene)
Cl
chlorobenzene
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You Try These!
• Name the following aromatic
compounds.
Br
CH2CH3
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Answers to You Try These!
• Name the following aromatic
compounds.
Br
Bromobenzene
CH2CH3
Ethylbenzene
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Common Aromatic
Compounds You Should Know
Nitrobenzene
NO2
Phenol
OH
Toluene
CH3
Aniline
NH2
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Naming Aromatic Compounds
When two groups are attached to benzene, the ring is
numbered to give the lower numbers to the side
groups. The prefixes ortho (1,2), meta (1,3) and para
(1,4) are also used.
Cl
CH3
Cl
CH3
Cl
CH3
ortho-dimethylbenzene
meta-dichlorobenzene
para-chloromethylbenzene
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Some Common Names
Some substituted benzene rings also use a common
name. Then naming with additional more side groups
uses the ortho-, meta-, para- system.
CH3
CH3
Toluene
Cl
m-chlorotoluene
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Some More Common Names
OH
NO2
OH
Phenol
p-nitrophenol
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Other Common Aromatic
Compounds You Should Know
CH
Cl3
Xylene
Cl 3
CH
OH
CH3
Cresol
Cl 3
CH
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You Try These!
Select the names for each structure:
Cl
1. Chlorocyclohexane
2. Chlorobenzene
3. 1-chlorobenzene
CH 3
CH 3
1. Meta-methyltoluene
2. Meta-dimethylbenzene
3. 1,3-dimethylbenzene
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Answers to You Try These!
Select the names for each structure:
Cl
2. Chlorobenzene
CH 3
1. Meta-methyltoluene
2. Meta-dimethylbenzene
3. 1,3-dimethylbenzene
CH 3
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You Try these!
Write the structural formulas for each of the
following:
A. 1-bromo-3-methylbenzene
B. Ortho-chlorotoluene
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Answers to You Try These!
Write the structural formulas for each of the
Br
following:
A. 1-bromo-3-methylbenzene
CH3
CH3
B. Ortho-chlorotoluene
Cl
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Homework Assignment
Pg. 345-346 12.11 – 12.12
Due Tomorrow!
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