NMR spectral study of some 2r,6c-diarylpiperidin-4-one (3′-hydroxy-2′-naphthoyl)hydrazones with special reference to γ-syn effect

1H and 13C NMR spectra have been recorded for 2r,6c-diarylpiperidin-4-one (3′-hydroxy-2′-naphthoyl)hydrazones 10-17 and 3,3-dimethyl-2r,6c-bis(p-methoxyphenyl)piperidin-4-one (5). For selected compounds 2D NMR spectra have been recorded. The spectral data along with those reported for related compounds are used to study the effect of a heteroatom X on the 13C chemical shift of a γ-carbon with X Cα Cβ Cγ torsional angle close to 0°, termed as γ-syn effect. Also γ-gauche and δ-effects of the alkyl groups at C-3 on the carbons of the aryl group at C-2 have been studied. The chemical shifts for the naphthalene ring are in accord with the mesomeric and steric effects of the carbonyl and hydroxy groups.