A Theoretical Approach to Substituent Effects. Examination of Phenoxides and Anilides as Models for Benzyl Anions

Ab initio molecular orbital calculations with the minimal STO-3G basis set have been carried out for a series of meta- and para-substituted benzyl and anilide anions with substituents CH3, NH2, OH, OCH3, F, N02, CN, CHO, and CF3. The results are analyzed in terms of substituent interactions and compared with previously reported data for toluenes, anilines, phenols, and phenoxide anions. The results suggest that (a) substituted phenoxide anions are useful models for substituent effects in corresponding benzyl anions in the gas phase, (b) effects of substituents on acidities of toluenes, anilines, and phenols are largely due to substituent interactions in the anions and only to a smaller extent to interactions in the neutrals, (c) the sensitivity of acidity to substituent change increases slightly in the order anilines < phenols < toluenes due in part to substituent effects in the neutrals, and (d) differences in the solution behavior of substituted phenoxide and benzyl anions stem from the large differences in solvent effects for these two systems.