Chemical shifts and charge densities in substituted nitrosobenzenes

The previous observed anomalous ¹³C-NMR chemical shifts of a series of para-substituted nitrosobenzenes have been investigated using Molecular Orbital calculations with the semi-empirical CNDO/2 method and at the STO-3G basis level. The calculations show atomic electron populations at C-4, the position of attachment of the nitroso group, analogous to those found for the corresponding position in monosubstituted benzenes. Thus, groups such as CN and NO₂ lead to a decrease in the p-electron population at this position. It thus seems that the observed unexpected upfield shifts found at C-4 for these substituents is not a function of unusual electron distribution in nitrosobenzenes. The possibility of differing conformations in the nitrosobenzene group has also been found unlikely. © 1988.