Discussion of standard nitration rates for benzenoid and heteroaromatic compounds

Standard log ko values for nitration are compared with previous partial rate factors. log ko values for mono-substituted benzenes are correlated by σ+ with ρ–9.7, but for polysubstituted derivatives and heterocyclic analogues much scatter is shown which is not improved by a correction term of type πσ+ for substituent-substituent interactions. Comparison of relative reactivities of individual substrates towards nitration and to hydrogen exchange shows that there is no simple unique scale of substrate reactivity toward electrophilic substitution.