The Molecular Conformation of 1e,2a,6e-Trimethyl-4e-phenyl-4a-acetoxypiperidine Hydrobomide in the Crystalline State

The title compound represents one analog of the synthetic 4-phenylpiperidine narcotic analgesics. The crystal structure was determined by the heavy-atom method from data collected on an automated diffractometer. The crystals are monoclinic, space group P21/c, with unit cell dimensions a = 11.833 A, b = 11.551 A, c = 14.659 A and β = 121° 9′. The final residual, R, was 0.056. The stereochemistry of the substituents on the piperidine ring as deduced by this structural determination (1e,2a,6e-trimethyl-4e-phenyl-4a-acetoxypiperidine) confirms the p.m.r. results on the alcohol precursor as trans 2-Me/6-Me and trans 2-Me/4-Ph. There is a normal length N—H … Br hydrogen bond of 3.234 A; most intramolecular bond lengths and angles are within the expected ranges but some distortion of the ideal chair conformation of the piperidine ring occurs.