Stereochemistry of the heterocyclic alcohols containing piperidine unit

The stereochemistry of the heterocyclic alcohols (1-4) containing piperidin e unit was studied on the basis of the results of molecular mechanics and q uantum chemistry calculations, The results showed that there existed the no n-classical orbital super-conjugated interactions between the nitrogen atom and oxygen atom which caused the conformations to be more stable when the hydroxylic group lay at axial than at equatorial with respect to the piperi dine ring in compound 1 and compound 3, If the axial hydrogen atoms at C-2 and C-6 positions in the piperidine ring were substituted, or the molecular existed in the polar solutions, this non-classical orbital super-conjugate d interactions would he much weak even diminished. In this case, the confor mations were more stable when the hydroxylic group at equatorial than at ax ial in these compounds.