Abstract

The opposite polarizability and inductive effects of the substituent groups on the gas phase acidity of alcohols and silanols are analyzed on the basis of a simple model that relates the proton affinity to the dipole polarizability. Inductive (electrostatic) effects are represented in terms of the variation in electronic chemical potential mediated by local softness at the basic center of the conjugated bases. Electronic (polarization) effects may be probed by the variations in local softness at the basic site. In alkyl alcohols, polarizability effects outweigh inductive effects, while in the corresponding silanol series, the opposite trend is observed. These results are in agreement with the experimental model of substituent effects proposed by Damrauer et al. (J. Am. Chem. Soc. 1991, 113, 4431): alkyl groups decrease silanol acidity, in contrast to alkyl group effects in alcohols.