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.