PROTON TRANSFERS IN DIPOLAR APROTIC SOLVENTS .V. SOLVATION AND GEOMETRIC FACTORS IN RATES OF PROTON TRANSFER REACTIONS

Data concerning the rates and equilibria of carbon acid-base reactions in methanol and dimethyl sulfoxide solutions are presented and interpreted to arrive at the following conclusions. (1) The p7Ts of carbon acids of the fluorene or triphenylmethane types are approximately 6 pK units lower in DMSO than in methanol solution. (2) The slow rates of proton transfers involving carbon acids are due to energy requirements for both solvent and internal geometric reorganizations on going from the acid to a resonance-stabilized conjugate base. (3) Internal geometric reorganizations contribute to the activation energies for fluorene-type acids, but not to oxygen acids because of extreme differences in the abilities of the two types of acids to hydrogen bond to the proton acceptor and thereby stabilize the transition states. © 1969, American Chemical Society. All rights reserved.