Freeman M. Wong

Surprisingly low aqueous acidity at the alpha-positions of pyridiniums and pyrimidinium: the role of solvation.

The p K(a)s of the 6-CH groups of N-methyl-2-methoxypyridinium, N-methyl-4-methoxypyridinium, and 1-methyl-2,4-dimethoxypyrimidinium ions in aqueous solution were determined to be about 33. The p K(a) values were nearly identical to each other and surprisingly similar to those reported for the neutral pyridones and uracil. Further determination of the enthalpies and entropies of the H-D exchange reactions revealed the role of solvation.

Decarboxylation of 1,3-dimethylorotic acid revisited : Determining the role of N-1

Abstract The decarboxylation of 1,3-dimethylorotic acid was found to be only about two to three times as fast as that of citrazinic acid (1-deazaorotic acid). It is thus concluded that the positive charge development on the adjacent N-1 is not as important as previously proposed.

The strength of a low-barrier hydrogen bond in water

Abstract There are large differences between the acidity of the enol of the acyclic diketone, 2,4-pentanedione and those of two cyclic diketones, 1,3-cyclopentanedione and 1,3-cyclohexanedione. Computational studies have demonstrated that these differences are largely due to the strength of the internal low-barrier hydrogen bond (LBHB) in the enol of 2,4-pentanedione. It is thus estimated that the lower limit of the additional free energy of formation in water for this LBHB over that of a conventional hydrogen bond is 4.1–5.3 kcal mol −1 .