¹³C NMR spectroscopic studies of C-nitroso compounds. The orientation of the nitroso group in substituted nitrosobenzenes

The carbon-13 chemical shifts of several substituted nitrosobenzenes are reported. It is shown that the NO group can be orientated to lie in the plane of the ring when constrained either by a bulky ortho substituent or in the solid state. In the presence of 2.6-di-tert-butyl substituents the NO group is twisted into orthogonality with the ring. The changes in the ¹³C chemical shifts are larger for the NO group than for other functional groups. It is suggested that these effects are a consequence of the electronic character of the NO group and that the nitrogen lone pair of electrons is of fundamental importance in producing these unique effects. The dimeric nitroso functional group does not display these properties.