Substituent Effects on the Protolytic Dissociation of Electronically Excited Phenols*

The aqueous dissociation of electronically excited singlet states of a series of mono‐substituted phenols has been investigated spectroscopically. Apart from the greatly enhanced acidity of these species resulting from excitation, the electronic effects of substituents are similar for ground and excited singlet state reactions. The dissociation constants for the excited state appear to be correlated with ground state values of the substituent constants. The possible generality of the Hammett equation for correlating the effects of substituents on the reactivity of excited singlet states is discussed.