Spin–spin coupling constants between carbon-13 and bromine in bromomethanes

Abstract

The dominant relaxation mechanism of the ¹³C nucleus in bromomethanes is the scalar coupling interaction owing to the fact that the resonance frequency of ¹³C 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 spin–spin coupling constants between ¹³C and ⁷⁹Br 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.