Proton and carbon nuclear magnetic relaxation in 2-bromothiophene

Abstract

Nonselective and semiselective inversion-recovery measurements are reported for the ring protons of 2-bromothiophene in 0.1 M solution with carbon disulfide. Density matrix analysis of the full recovery curves yields accurate values for autocorrelation parameters, but uncertainty with regard to residual nondipolar relaxation pathways limits the accuracy of dipolar cross-correlation terms. The proper choice of interaction strength (internuclear distance) for analyzing dipolar relaxation is discussed, and by requiring that proton and 13C relaxation yield consistent motional results, uncertainties with regard to interaction strengths can be reduced. It was not possible to obtain all elements of the 2-bromothiophene rotational diffusion tensor, but the ratio D yy / D xx = 2.0 ± 0.2 and the shift of rotational axes β = 20 ± 2° away from principal inertial axes were determined with reasonable precision.