Determination of rotational barriers of carbon-carbon bonds in 2‐arylpiperidines

Abstract
Carbon‐carbon sp3‐sp2rotational barriers of 3,3‐dimethyl‐2‐(3,4,5‐trimethoxyphenyl)‐4‐piperidones and their ethylene ketals have been evaluated using nmr techniques. The conformation of1hydrochloride has been studied by NOE determinations. Values found for the hydrochlorides of the title compounds are discussed in terms of equilibria with free bases and nitrogen inversion.