Theoretical Study of the Solvent Effect on Functional Group Properties and on the Charge Distribution and Acidity of Alkyl-Substituted Alcohols

Abstract

For a number of functional groups, the group electronegativity and hardness in the gas phase and in different solvents was calculated using the recently introduced self-consistent isodensity polarized continuum model (SCI-PCM). The results indicate that the groups become less electronegative and less hard with increasing dielectric constant. Using the calculated functional group properties and Sanderson's electronegativity equalization principle, charge distributions in the alkyl alcohols X−OH and their conjugated bases XO- (with X = −CH3, −CH2CH3, and −CH(CH3)2 are determined in solution. The calculated charge distributions are used in a study of the inversion of alkyl alcohol acidity from gas phase to aqueous solution. Relative acidities are calculated in the gas phase and in aqueous solution for methanol, ethanol, 2-propanol and tert-butanol. The experimentally observed inversion of the acidity sequences of these systems is reproduced, and special importance is assigned to the stabilization energy of the conjugate bases in both media.