Electrophilic Attack on Disubstituted Benzenes

Do the rules developed so far in this chapter predict the reactivity and regioselectivity of still higher substitution We shall see that they do, provided we take into account the individual effect of each substituent. Let us investigate the reactions of disubstituted benzenes with electrophiles. 

In trying to predict the regioselectivity of electrophilic substitution of disubstituted benzenes, we have to apply the same considerations that were necessary to understand the directing 

Guideline 1. The most powerful activator controls the position of attack (indicated by yellow arrows). 

Guideline 2. Experimentally, we can rank the directing power of substituents into three 

Guideline 3. In such cases where product mixtures are predicted on the basis of guidelines 1 and 2, you may typically discount those that constitute ortho attack to bulky groups or between two substituents (dashed black arrows). 

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