The rotational pathway of the phenyl ring in N, 3,3-trimethyl-2-phenyl-4-piperidone has been determined by molecular mechanics calculations to be chair piperidone ⇋ twist-boat piperidone ⇋ phenyl rotation. The calculated barrier height for the process (ca. 63 kJ/mol) is in good agreement with the previously reported experimental value of 54 kJ/mol in a remotely substituted phenyl derivative determined by 1H DNMR. © 1986, American Chemical Society. All rights reserved.