Configurational equilibria for a range of N-alkylpiperidine hydrochlorides in deuterium oxide or deuteriochloroform have been examined by n.m.r. spectroscopy. Where comparison with equilibria in analogous cyclohexane systems is possible, higher proportions of the less stable configurations are observed in the hydrochloride solutions. Rapid â irreversibleâ acidification of the N-alkylpiperidines (for example, with trifluoroacetic acid) gives configurational ratios for the resulting solutions which are not necessarily the same as the conformer ratios corresponding to N-alkyl flip for the neat, liquid bases.