Electrostatic effects in ionization equilibria: An MNDO study of proton and hydrogen transfer reactions of 4-fluorobutanol

Abstract

MNDO molecular orbital calculations have been carried out for sp and ap conformers of 4-fluorobutanol and some 4-X-bicyclo[2.2.2]octanols (X = F, Cl). The results are analyzed in terms of substituent effects on proton transfer enthalpies δ ΔH0 and homolytic bond dissociation energies δDH0 (A-H) and compared with the previously reported data for 5-fluoropentanoic acid and 4-fluorobutylamine. The results are further compared with the prediction of the electrostatic theory. It is shown that the substituent polar effect FD on the acidities of halogenoalcohols is largely due to substituent interaction in the anions and only to a smaller extent to interactions in the neutral alcohol. A small contribution (about one-tenth for the ap conformer) is probably also made by the substituent effects on homolytic bond dissociation energies DH0 (A-H).