ABINITIO STUDY OF THE NITROGEN LONE-PAIR PROXIMITY EFFECT ON A METHYL C-H BOND IN 2-METHYLPYRIDINE

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 of that 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.