Kinetics of proton transfer from cationic carbon acids in water and aqueous DMSO. Effect of activating groups and solvent on intrinsic rate constants.

[reaction: see text] Acidity constants and rates of reversible deprotonation of acetonyltriphenylphosphonium ion (1H+), phenacyltriphenylphosphonium ion (2H+), N-methyl-4-phenacylpyridinium ion (3H+), and N-methyl-4-(phenylsulfonylmethyl)pyridinium ion (4H+) by amines in water, 50% DMSO-50% water (v/v), and 90% DMSO-10% water (v/v) have been determined. From the respective Brønsted plots, log k(o) values for the intrinsic rate constants of the various proton transfers were obtained. Solvent transfer activity coefficients of the carbon acids and their respective conjugate bases were also determined which helped in understanding how the pKa values and intrinsic rate constants depend on the solvent.

Kinetics of Proton Transfer from Benzoylnitromethane and 1,2-Diphenyl-2-nitroethanone to Various Bases. Resonance, Inductive, Solvation, Steric, and Transition State Hydrogen-Bonding Effects on Intrinsic Rate Constants.

The replacement of a hydrogen in nitromethane and in phenylnitromethane by the PhCO group has a strong acidifying effect, i.e., PhCOCH(2)NO(2), 5, is 5.