chapter 12 alkenes, alkynes, and aromatic compounds

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1

Chapter 12 Alkenes, Alkynes, and Aromatic Compounds

12.5 Aromatic Compounds


Benzene has 6 electrons shared equally among the 6 C atoms is also represented as a hexagon with a circle drawn

inside

Benzene Structure


Aromatic Compounds in Nature and Health


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


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


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-


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

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Xylene

For isomers of dimethylbenzene, the common name xylene may be used

8


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


Solution

Select the correct name(s) for each of the following compounds:

2) chlorobenzene

2) 1,3-dimethylbenzene3) m-xylene

CH3

CH3

Cl


Learning Check

Draw the condensed structural formulas for each of the following:A. 1,3-Dichlorobenzene

B. o-Chlorotoluene


Solution

Draw the condensed structural formulas for each of the following: A. 1,3-Dichlorobenzene

B. o-Chlorotoluene

Cl

Cl

CH3

Cl


Learning Check

Identify the organic family for each of the following:

A. CH3─CH2─CH═CH2

B.

C. CH3─C≡CH

D.


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


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


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


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


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


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


Learning Check

Write the equation for the bromination of benzene, including the catalyst.


Solution

Write the equation for the bromination of benzene, including the catalyst.

HBr+

FeBr3

Br

Br2+

H

chapter 12 alkenes, alkynes, and aromatic compounds

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