DYNAMIC NMR-STUDY OF THE FACTORS GOVERNING NITROSO GROUP ROTATION IN P-NITROSOANILINES IN THE SOLUTION AND SOLID STATES

The energy barriers associated with N=O rotation in a series of p-nitrosoanilines were measured by the total bandshape NMR method. Energies [Delta G(double dagger) (298.15 K)] are in the range 38-57 kJ mol(-1), the magnitudes being lowered appreciably by the presence of methyl substituents flanking the nitroso group on either side. In the case of p-nitroso-N,N-dimethylaniline, N=O rotation has been shown to occur also in the solid state with a slightly higher energy barrier to that in the dissolved state, For p-nitroso-N-methylaniline, a combination of 2D-exchange spectroscopy (EXSY) and 1D-bandshape analysis NMR methods enabled the barriers to N=O rotation and NHMe rotation to be measured separately.