THE FRAGMENTATION OF PROTON-BOUND CLUSTER IONS AND THE GAS-PHASE ACIDITIES OF ALCOHOLS

The gas-phase acidities of 52 alkanols and cycloalkanols have been determined from studies of the unimolecular and collision-induced dissociation of proton-bound cluster ions [RO...H...OR']-. It is found that CH3OH is 0.6 kcal mol-1 more acidic (lower DELTAH-degrees(acid) value) than CD3OH, while C2H5OH is 0.6 kcal mol-1 more acidic than C2D5OH. A detailed evaluation of the effect of methyl substitution alpha, beta and gamma to the oxygen on the acidities of the alcohols is presented, as well as an evaluation of the role of charge-induced dipole interactions on gas-phase acidities. The DELTAH-degrees(acid) values for stereoisomeric methylcyclohexanols are reported. cis-Methyl groups lower the DELTAH-degrees(acid) values of the alcohols, the cis-2-methyl group showing the largest effect. The trans-2-methyl group also increases the acidity but trans-methyl groups in the 3 and 4 positions have no effect on the acidity of the cyclohexanol.