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Chapter 12 Alkenes, Alkynes, and Aromatic Compounds
12.5 Aromatic Compounds
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Benzene has 6 electrons shared equally among the 6 C atoms is also represented as a hexagon with a circle drawn
inside
Benzene Structure
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Aromatic Compounds in Nature and Health
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Naming Aromatic Compounds
Aromatic compounds are named with benzene as the parent chain with one side group named in front of benzene
Methylbenzene Chlorobenzene
ClCH3
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Some Common Names
Some substituted benzene rings have common names that have been used for many
years with a single substituent use a common name or are
named as a benzene derivative.
Toluene Aniline Phenol (methylbenzene) (benzenamine) (hydroxybenzene)
NH2 OHCH3
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Aromatic Compounds with Two GroupsWhen two groups are attached to a benzene ring, number the ring to give the lowest numbers to the
side groups (IUPAC)or use prefixes to show the arrangement of the
substituents (common) on the ringortho (o) for 1,2- meta (m) for 1,3- para (p) for 1,4-
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Examples of Aromatic Compounds with Two Groups
3-Chlorotoluene 1,4-Dichlorobenzene 2-Chlorophenol(m-chlorotoluene) (p-dichlorobenzene) (o-chlorophenol)
Substituent's on1st and 3rd carbons 1st and 4th carbons 1st and 2nd carbons
OHCH3
Cl
Cl
Cl
Cl
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Xylene
For isomers of dimethylbenzene, the common name xylene may be used
8
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Learning Check
Select the correct name(s) for each of the following compounds:
1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene
1) 1,2-dimethylbenzene2) 1,3-dimethylbenzene3) m-xylene
CH3
CH3
Cl
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Solution
Select the correct name(s) for each of the following compounds:
2) chlorobenzene
2) 1,3-dimethylbenzene3) m-xylene
CH3
CH3
Cl
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Learning Check
Draw the condensed structural formulas for each of the following:A. 1,3-Dichlorobenzene
B. o-Chlorotoluene
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Solution
Draw the condensed structural formulas for each of the following: A. 1,3-Dichlorobenzene
B. o-Chlorotoluene
Cl
Cl
CH3
Cl
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Learning Check
Identify the organic family for each of the following:
A. CH3─CH2─CH═CH2
B.
C. CH3─C≡CH
D.
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Solution
Identify the organic family for each of the following:
A. CH3─CH2─CH═CH2 alkene
B. cycloalkane (alkane)
C. CH3─C≡CH alkyne
D. aromatic
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Properties of Aromatic CompoundsAromatic compounds have a stable aromatic bonding system are resistant to many reactions undergo substitution reactions, which retain
the stability of the aromatic bonding system
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Substitution Reactions
In a substitution reaction, a hydrogen atom on a benzene ring is replaced by an atom or group of atoms.
Type of substitution H on benzene replaced by Halogenation Chlorine or bromine atom Nitration Nitro group (—NO2)
Sulfonation —SO3H group
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Halogenation
In the halogenation of benzene an H atom of benzene is replaced by a chlorine or
bromine atom a catalyst such as FeCl3 is needed in chlorination a catalyst such as FeBr3 is needed in bromination
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Nitration
In the nitration of benzene, an H atom of benzene is replaced by a nitro (–NO2)
group from HNO3 an acid catalyst such as H2SO4 is needed
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Sulfonation
In the sulfonation of benzene, an H atom on benzene is replaced by a —SO3H
group from SO3 an acid catalyst such as H2SO4 is needed
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Learning Check
Write the equation for the bromination of benzene, including the catalyst.
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Solution
Write the equation for the bromination of benzene, including the catalyst.
HBr+
FeBr3
Br
Br2+
H