NMR RELAXATION STUDY OF MOLECULES CONTAINING A CO GROUP - DETERMINATION OF THE O-17 QUADRUPOLAR COUPLING-CONSTANT AND OF THE C-13 SHIELDINGTENSOR ANISOTROPY IN SOLUTION

The NMR relaxation times of the C-13(O) nuclei of formanilide, acetani lide, benzamide, benzoic acid, the benzoate anion and glycine were mea sured for four different magnetic field values, allowing the determina tion of the contribution of the shielding anisotropy mechanism to the total relaxation rate. The knowledge of the reorientational correlatio n time of the molecules, determined from measurements of the C-13 rela xation time of a C-13-H fragment, the motion of, which is not affected by internal rotations, allowed the calculation of the anisotropy of t he C-13(O) shielding tensor, Delta sigma. From the linewidth of the O- 17 NMR signals it was also possible to deduce the O-17 quadrupolar cou pling constant, chi, of the oxygen nucleus in the CO group. The values of Delta sigma and chi were obtained in solution and were compared wi th those obtained in the solid state; with the exception of benzoic ac id, the Delta sigma values for solutions and solids are similar, The r elaxation processes were analysed in detail and the Delta sigma and ch i values are discussed.