A Molectll9r Orbital Discussion of the Hammett Equation Semi-empirical Interpretation on the Abnormality of the Benzyl Anion Type Substituent

This paper presents a semi-empirical consideration on the abnormality of the Benzyl anion type substituent in electrophilic aromatic substitutions from the standpoint of the simple molecular orbital theory. Substituent effects in nucleophilic and radical reactions are also discussed. Serious deviations from the Hammett equation are often observedle for some benzyl anion type substituents such as CH3O or N(CH3)2, in electrophilic reactions. In the previous paper,le ' we proposed that another series of the substituent con-stants ((lc) are to be used in the electrophilic reactions. This paper presents a semi-empirical consideration on the abnormality of the benzyl anion type substituents in electrophilic reactions from the standpoint of the simple molecular orbital theory. In this connection, substituent effects in nucleo-philic and radical reactions are also discussed. The rate constant k of a chemical reaction is given by Eq. (1) or (2): h=Ae`dIPIRT(1) h = r k eaS*IRe-21-1*/R7'(2),