A Guidebook to Mechanism in Organic Chemistry

The Effect of a Substituted already Present

Direction in

Y

OH 1-6

NH, 1-5

OMe 1-2 *-+

Me 0-3

H 00

ci 1-6

CHO 2-8 +-*•

SO,H 3-8

NO, 3-9

the axis of the benzene ring and hence the component of the moment

actually affecting the bond to the ring may thus be different from the

observed moment of the molecule as a whole: ^

The relation between electron-availability and ease of electrophilic
substitution may, however, be seen by comparing the direction and
magnitude of dipole moments (p. 119) with the following relative
rates of attack by ®N0 2 :

PhOH PhMe PhH PhCl PhNO,

103 2-5 1 3xl0-a < 10-«

(iv) The position* of substitution

Which position, o-, m- or p- is actually entered by the incoming group
will depend on which leads to the most readily formed transition state.