13C NMR spectral behavior of N-substituted-4-piperidones in methanol. Possibility of distinguishing between acetal and hemiacetal.

The behavior of several N-substituted-4-piperidones in methanol has been studied by 13C nuclear magnetic resonance (NMR) spectroscopy. All the piperidones studied were found to be equilibrium with their hemiacetals in methanolic solutions. The features of N-acyl derivatives were different from those of N-alkyl derivatives and the differences could be accounted for by electronic factors. The chemical shifts of the acetals were also determined and a procedure for distinguishing between hemiacetal and acetal is proposed.