The static and Dynamic NMR spectra of 4,4′‐bis(N‐isopropyl‐N‐nitrosoamino)biphenyl, a four‐site exchange problem

Abstract

The 'H and 'jC NMR spectra of 4,4'-bis(N-isopropyl-N-nitrosoamino)biphenyl at 22 "C were consistent with the presence of three isomers due to slow rotation about the N-N bonds of the two N-nitroso groups. The structures of the three isomers were assigned by means of their symmetries and from the known effects of the two orientations of the N-nitroso group on ' H and "CNMR chemical shifts. Each conversion of an N-nitroso group from anti to syn to an aryl group was associated with the same free energy ditference (0.26 kcal mol-') after symmetry corrections were made. The changes in the "C NMR spectra recorded from 95 to 150 "C were simulated using a program for classical four-site exchange. The potential barrier to rotation was calculated to be 20.76 It 0.06 kcal mo1-l at 400 K.