Stereochemistry of the Heterocyclic Alcohols Containing Piperidine Unit

The stereochemistry of the heterocyclic alcohols (R₁-OH~R₄-OH,see Fig.1) containing piperidine unit has been studied on the basis of the calculations of molecular mechanics and quantum chemistry. The calculations of alcohols (R₁-OH~R₄-OH) and their carboxylate derivatives were carried out, and the results of these calculations were listed in Tab.1 and Tab.2. It was showed that there existed the non-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 piperidine ring in compounds (R₁-OH) and (R₃-OH). If the axial hydrogen atoms at C₂ and C₆ positions in the piperidine ring were substituted, or the molecular existed in the polar solutions, this non-classical orbital super-conjugated interactions would be much weak even diminished. In this case,the conformations were more stable when the hydroxylic group at equatorial than at axial in these compounds. These consistented with the experimental results.