Electrophile affinity: a reactivity measure for aromatic substitution

The literature data for the partial rate factors and (ln) for [S.sub.E]Ar processes are compared to theoretical reactivity parameters to rationalize the reactivity and regioselectivity of the electrophilic chlorination, nitration, and alkylation of benzene derivatives. The observed variations of electron density at the different arene ring positions and the experimental partial rate factors for the chlorination and nitration reactions are attributed to strong steric influences on the reaction rates for substitutions involving the bulky benzyl moiety.