The 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre: Simple means to characterize the electron distribution of carbenes.

Abstract

Both the 13 C chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and 13 C chemical shifts were calculated and compared with the experimental δ(13 C)/ppm values and geometry parameters (as a quality criterion for obtained structures).