Recipient of NIH Research Career Development Award (1982–1987).
Effects of alkylation upon the proton affinities of nitrogen and oxygen bases
Article first published online: 7 SEP 2004
Copyright © 1984 John Wiley & Sons, Inc.
Journal of Computational Chemistry
Volume 6, Issue 3, pages 168–172, June 1985
How to Cite
Redfern, P. and Scheiner, S. (1985), Effects of alkylation upon the proton affinities of nitrogen and oxygen bases. J. Comput. Chem., 6: 168–172. doi: 10.1002/jcc.540060303
- Issue published online: 7 SEP 2004
- Article first published online: 7 SEP 2004
- Manuscript Accepted: 15 NOV 1984
- Manuscript Received: 16 SEP 1984
The protonation energies of alkylated derivatives of NH3 and OH2 are calculated at the Hartree–Fock level with the split-valence 4-31G basis set. The methyl, dimethyl, and ethyl amines are studied; oxygen bases include methanol, dimethylether, and ethanol. The geometries of each molecule and its protonated analog are fully optimized. It is found that protonation leads to significant changes in the molecular structures. In particular, the bonds to the N and O atoms are substantially elongated, especially when the other atom involved is C rather than H. The calculated absolute proton affinities are somewhat larger than the experimental values. However, the differences in protonation energies of the various molecules relative to one another agree quantitatively with experiment. Replacement of one H atom of the base by a methyl group induces an increase in proton affinity of some 10 kcal/mol. If a second methyl group is added to the N or O atom, a further increment of about 70% this amount is noted. On the other hand, placement of the second C atom on the first methyl group (to form an ethyl substituent) leads to a smaller increase (∼30%). The magnitudes of these alkyl substituent effects are somewhat larger for the oxygen bases than for the amines.