Studies on 13C Magnetic Resonance Spectroscopy. XV. Correlation between 13C NMR Chemical Shifts and Charge Densities of Diaza-Benzenes

Charge densities of diaza-benzenes-2-substituted pyrazines, 5-substituted pyrimidines and 4-substituted pyridazines-were calculated by the MINDO/2 method. The correlations of the substituent-induced 13C chemical shifts (13C SCS) values of these three diaza-benzenes with total charge densities were determined, and linear relations between the two parameters were found even at the ipso position, whereas the correlations of the ipso SCS with a linear combination of substituent constants were poor.