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Abstract:
The 17O quadrupole-coupling tensor in a single crystal of benzophenone was completely determined using high-field NMR, with B0 of 8.4 T. The sample crystals were 50% 17O enriched; the carbon in the carbonyl position was 90% 13C. All possible transitions of the 17O nucleus were observed. The 17O quadrupole-coupling tensor (QCT) was determined from the and the quadrupole splittings. The quadrupolecoupling constant and asymmetry parameter are ezgQih = 10.808 MHz and η = 0.369. The principal axis system of the QCT conforms to the local C2v symmetry of the carbonyl group. The fine structure of the 17O transitions, caused by 17O13C coupling, allowed determination of the 17O13C coupling tensor. The resulting CO distance r = 1.213Å agrees well with the X-ray data. By taking into account the second-order quadrupole shifts the 17O chemical-shift tensor could be determined from the trasitions. The principal axis that corresponds to the largest paramagnetic shift is parallel to the CO bond. The largest diamagnetic shift is perpendicular to the-CO plane. These findings are in good agreement with a Hartree-Fock calculation on the related compound formaldehyde.
