Organic Chemistry

Section 16.4 The Effect of Substituents on Orientation 637

anisole

Y

H

Y

H

Y

H

Y

H

Y

H

Y

H

Y

H

H Y H Y H Y H Y

OCH 3

+ Y+

OCH 3

OCH 3 OCH 3 OCH 3

OCH 3 OCH 3 OCH 3

OCH 3

OCH 3 OCH 3

ortho

meta

para

relatively stable

relatively stable

++

+ +

+

++

+

+

OCH 3

+

+

Figure 16.2
The structures of the carbocation intermediates formed from the reaction of an
electrophile with anisole at the ortho, meta, and para positions.

Y

H

Y

H

Y

H

Y

H

Y

H

Y

H

H Y H Y H Y

+ Y+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

NH 3

+

ortho

meta

para

least stable

least stable

protonated

aniline

+ +

+

++

+ +

+

+

Figure 16.3
The structures of the carbocation intermediates formed from the reaction of an
electrophile with protonated aniline at the ortho, meta, and para positions.

Notice that the three possible carbocation intermediates in Figures 16.1 and 16.3 are
the same, except for the substituent. The nature of the substituent determines whether the
resonance contributors with the substituent directly attached to the positively charged