13C NMR spectra have been recorded for eleven piperidin-4-one oximes and for seven of them 1H NMR spectra have been recorded at 270 MHz The effect of oximation on the NMR chemical shitts is discussed The conformations of the oximes are also discussed, based on the observed chemical shifts Although several oximes appear to adopt a chair conformation, in the same manner as the corresponding ketones, the oximes of 3,5-dimethyl-2,6-diarylpiperidin-4-ones with cis-methyl groups seem to adopt an asymmetric non-chair conformation Analysis of the chemical shifts of cis-2,6-dimethylcyclohexanone oxime suggests that this compound also exists in a non-chair conformation, and not in a chair conformation with two axial methyl groups as suggested previously

13C and 1H NMR spectral studies of some piperidin-4-one oximes

Synthesis and NMR spectral studies of N-chloroacetyl-2,6-diarylpiperidin-4-ones.

Synthesis, spectral, stereochemical, single crystal XRD and biological studies of 3t-pentyl-2r,6c-diarylpiperidin-4-one picrate derivatives

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

13C NMR spectra of six epimeric substituted 4-hydroxypiperidines and two corresponding piperidines were recorded. Substituent parameters for equatorial methyl, gem-dimethyl, equatorial hydroxy and axial hydroxy groups were calculated from the 13C chemical shifts of these compounds and several other six-membered ring compounds. The effects of nearby substituents on these parameters were examined. It is concluded that the magnitude and even the sign of the α effect is modified by the presence of nearby substituents. It was found that gauche interactions play an important role in determining the magnitude of the α effect. However, the β effect is not influenced by the nearby substituents except for the gem-dimethyl group. The magnitude of the γ effect is almost independent of the nearby substituents.

Influence of gauche interactions on the substituent effects on carbon-13 chemical shifts in six-membered ring compounds

The 13C NMR spectra of several methyl substituted 2,6-diaryl-4-piperidones (aryl = phenyl, o-chlorophenyl) have been measured. Substituent parameters for methyl and chloro groups have also been derived and are discussed in terms of their steric and electronic interactions. Both the methyl substitution at C-3 and chlorine substitution in the ortho position of the phenyl ring cause significant changes in the 13C chemical shifts, which can be satisfactorily explained on the basis of steric interactions taking place in the preferred conformations of these molecules. In compounds with o-chloro groups, the aryl ring is oriented such that the chlorine is syn to the axial hydrogen on the aryl-bearing carbon. The shielding effect of the carbonyl group is found to be more pronounced on an adjacent equatorial methyl than on an adjacent axial methyl group.

Dale Marko

Papers

Conformational analysis and 13C NMR spectra of some 2,6-diarylpiperidin-4-ones