A conformational analysis of 1‐arylpiperazines and 4‐arylpiperidines is presented using molecular‐mechanics and semi‐empirical calculations. It has been found that electronic effects of substituents on the aryl ring determine the conformational behaviour of 1‐arylpiperazines. Steric effects play a minor role. Electron‐withdrawing substituents on the aryl moiety increase the conjugation between the anilino nitrogen lone pair and the π electrons of the aryl group and direct the orientation between the aryl and heterocycle towards the same plane. Electron‐releasing substituents have the opposite effect and reduce the energy difference between a coplanar and perpendicular orientation between the rings. 4‐Arylpiperidines prefer a perpendicular orientation between the rings.
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Gerard Dijkstra (1993) studied this question.
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