19. Reactions of Aromatics: EAS and Beyond

Propose a mechanism for nitration of pyridine at the 4-position,

and show why this orientation is not observed.

Before spectroscopy was invented, Körner’s absolute method

was used to determine whether a disubstituted

benzene derivative was the ortho, meta, or para isomer.

Körner’s method involves adding a third group

(often a nitro group) and determining how many isomers

are formed. For example, when o-xylene is nitrated

(by a method shown in Chapter 17), two isomers are formed.

<IMAGE of reaction>

(a) How many isomers are formed by nitration of m-xylene?

Before spectroscopy was invented, Körner’s absolute method

was used to determine whether a disubstituted

benzene derivative was the ortho, meta, or para isomer.

Körner’s method involves adding a third group

(often a nitro group) and determining how many isomers

are formed. For example, when o-xylene is nitrated

(by a method shown in Chapter 17), two isomers are formed.

<IMAGE of reaction>

(b) How many isomers are formed by nitration of p-xylene?

Before spectroscopy was invented, Körner’s absolute method

was used to determine whether a disubstituted

benzene derivative was the ortho, meta, or para isomer.

Körner’s method involves adding a third group

(often a nitro group) and determining how many isomers

are formed. For example, when o-xylene is nitrated

(by a method shown in Chapter 17), two isomers are formed.

<IMAGE of reaction>

(c) A turn-of-the-century chemist isolated

an aromatic compound of molecular formula C6H4Br2.

He carefully nitrated this compound and purified three isomers

of formula C6H3Br2NO2. Propose structures for

the original compound and the three nitrated derivatives.

Give the structures of compounds A through B in the following series of reactions.

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Predict the major products formed when benzene reacts (just once) with the following reagents.

(j) nitric acid + sulfuric acid

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

(b) Predict the mononitration products of the following compounds

(i) <IMAGE>

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

(b) Predict the mononitration products of the following compounds

(iii) <IMAGE>

What product(s) result from nitration of each of the following?

e. benzenesulfonic acid

f. cyclohexylbenzene