Influence of intramolecular hydrogen bonding on the electronic structure of oxymorphone.

Approximate ab initio molecular orbital methods are used to examine the structural and electronic properties of oxymorphone. The most stable conformation of the molecule is found to include an intramolecular hydrogen bond between the C-14 hydroxyl group and the nitrogen atom in agreement with available experimental data. The total molecular electron density is transformed to a set of localized molecular orbitals, one of which corresponds to the lone electron pair on nitrogen. The hydrogen bond is shown to produce substantial bending and stretching of the lone pair when compared to its shape when such hydrogen bonding is precluded.