BR-79,BR-81 EFFECTS IN THE HIGH-RESOLUTION C-13 NMR-SPECTRA OF SOLID BROMOAROMATIC COMPOUNDS - DIPOLAR AND INDIRECT (BR-79,BR-81,C-13) INTERACTIONS STUDIED BY INVERSE FIRST-ORDER PERTURBATION-THEORY

Splittings in the C-13 cross-polarization magic angle spinning spectra of 1, 4-dibromobenzene and 4-bromo-3,5-dimethylpyrazole are reported. They arise from (Br-79,Br-81,C-13) interactions influenced by the qua drupolar nature of the bromine nuclei. They are analysed using both 'i nverse' perturbation and exact theories to yield data on both isotropi c and anisotropic coupling, including the signs. The spectra also enab le the sign of the bromine quadrupole coupling constant to be confirme d as positive.