Carbon-13 nuclear magnetic resonance studies of piperidine and piperazine compounds. Part II. Empirical substituent parameters for, and the shielding anisotropy of, the N-nitroso-group

Abstract

The carbon-13 chemical shifts have been measured for a number of substituted nitroso-piperidines and -piperazines. Complete assignments have been made and substituent parameters derived which allow reasonably accurate prediction of the chemical shifts in the molecules studied. The theories available for calculating the effect of the electric field, generated by the presence of the polar NO group, on the chemical shifts have been applied in a critical way for these molecules. The possibility of alternative formulations of electric field effects has been suggested and the limitations of studying small numbers of molecules in this respect assessed.