Conformation and tautomerizm of the 2-methyl-4-pyridin-2'-yl-1,5-benzodiazepine molecule. An ab initio study.

The protomeric tautomerizm and conformation of the 2-methyl-4-pyridin-2'-yl-1,5-benzodiazepine molecule were investigated, and its three neutral tautomers (B1,B2,B3) and their rotamers (C1,C2,C3) were considered. Full geometry optimizations were carried out at the HF/6-31G* and B3LYP/6-31G* levels in gas phase and in water. The tautomerization processes in water (epsilon = 78.54) were studied by using self-consistent reaction field theory. The calculation showed that the boat conformation is dominant for the seven-membered diazepine ring in all of the structures, even with different double bond positions. The calculated relative free energies (DeltaG) showed that the tautomer C(1) was the most stable structure, and its conformer B(1) was the second most stable in the gas phase and in water.