Spinndash;spin coupling constants between carbonhyphen;13 and bromine in bromomethanes

摘要

The dominant relaxation mechanism of the13C nucleus in bromomethanes is the scalar coupling interaction owing to the fact that the resonance frequency of13C is close to that of bromine and that bromine has its relaxation mechanism by the quadrupole interaction. The relaxation curves for bromomethanes show the nonexponential decay because of the presence of two bromine isotopes with the ratio of about 1:1. By analyzing the relaxation curves the spinndash;spin coupling constants between13C and79Br are found to be 95, 127, and 151 Hz for CD2Br2, CDBr3, and CBr4, respectively. From the bromine relaxation times obtained simultaneously in the analysis, the reorientational motion of bromoform is discussed and compared with that of chloroform.