Dielectric studies of H-bonded complexes of 2,6 diphenyl piperidones with phenols

The experimental values of the dipolar increments of the complexes of 2,6 diphenyl piperidin-4-one and 3,5 dimethyl 2,6 diphenyl piperidin-4-one with 2,3,5 trimethyl phenol, p-cresol, p-chlorophenol, 2,4 dichlorophenol and p-nitrophenol in dilute solutions of carbon tetrachloride were determined at 303K at 2MHz. The preferred orientation of the piperidones is a chair conformation with a slight flattening of the ring on methyl substitution and the nitrogen lone pair is equatorial to the heterocyclic ring. The dipolar increment is consistent with pKa values if theta(b), is taken in the vicinity of 90degrees which implies that H-bond formation is between the O-H group and the N-atom rather than the carbonyl oxygen. The through bond interaction in piperidones is found to be quenched by methyl substitution. (C) 2002 Elsevier Science B.V. All rights reserved.