Nuclear Quadrupole Resonance Studies of Charge-Transfer Complexes of Carbon Tetrabromide with Methyl-Substituted Benzenes and Pyridines

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Abstract
The 81Br nuclear quadrupole resonance spectra have been examined for a series of complexes of CBr4 with methyl‐substituted benzenes and pyridines. The p‐xylene−CBr4 complex gives two lines as expected from the known structure, and the benzene–CBr4 spectrum is the same, with a lower splitting. The spectra of a number of other complexes of unknown structure do not correlate simply with these. Estimates of the direct crystal‐field gradients due to the charge distribution in the aromatics suggest that the direct field gradient effects are much too low to account for observed shifts in quadrupole frequencies. The temperature dependencies of the resonances in the p‐xylene and durene complexes have been studied. The p‐xylene complex follows the Bayer equation, but the durene complex requires the inclusion of a temperature dependence of the torsional frequency. Both complexes show a fading of the resonances at about 50° below the melting points.

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