| Sumario: | Ab initio optimized geometries for three different methyl conformations of 2-methylpyridine were analyzed in order to study the nitrogen lone-pair proximity effect on a methyl C-H bond. Calculations were carried out using three different basis sets in order to determine how far the description ofthat effect depends on the wave function quality. They are 4-31G, 4-31G** and 6-31G**. Results thus obtained are discussed in terms of the hyperconjugative and the N lone-pair proximity effects. For an all-cis conformation with respect to the N lone-pair, a shortening of the methyl C-H bond was found, together with a redistribution of the electronic density along that bond. © 1992.
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