Hydrogen Bond of 4-Amino-5H-[1]benzopyrano[3,4-c]pyridin-5-one Derivatives with Alcohols. II. Theoretical Considerations

Abstract

Abstract In a previous paper the experimental considerations on the hydrogen bonding between benzopyranopyridine derivatives including related compounds (pyridine, coumarin, and aniline) and alcohols were made, and the thermodynamic constants for the formation of the hydrogen-bonded complexes were obtained from UV spectroscopic studies. In this paper the molecular orbital calculation by the CNDO/2 method was conducted to further clarify the experimental results. Several conclusions were drawn from the present calculation: (1) Benzopyranopyridine has an intramolecular hydrogen bond between its amino and carbonyl groups. (2) The hydrogen bond energy of 2-alkyl benzopyranopyridines with alcohol is larger than that of the 1-alkyl compounds. (3) Benzopyranopyridine has four positions for hydrogen bond formation with alcohol, that is, the ring nitrogen atom, the carbonyl group, the ring oxygen atom, and the amino group. The ring nitrogen atom gave rise to the largest hydrogen bond energy among the four positions. Therefore, the corresponding hydrogen-bonded complex plays an important role in the benzopyranopyridine–alcohol system. (4) The hydrogen bond energy depended on the charge density of the atom which gave rise to the hydrogen bond with alcohol. Especially, substitution of the electron donating group such as amino and methyl groups at the position which increases the charge density of the atom giving rise to a hydrogen bond with alcohol increases the hydrogen bond energy.