Cross-correlation effects in the spin-lattice relaxation of ethanol methylene 13C

The spin-lattice relaxation of methyl and methylene 13 C and 1 H of ethanols CH 3 CH 2 OD and CD 3 CH 2 OD diluted with CD 3 CD 2 OD has been studied by the inversion-recovery method. Recovery of the proton spectral lines is described by a single exponential function with the same rate constant for all transitions. Intramolecular, intergroup and intermolecular contributions to the proton longitudinal relaxation have been determined using the concentration dependence of the relaxation rate of diluted samples. Methylene 13 C spectral lines are recovered non-exponentially with the different rates. This behaviour is caused by the interference or cross-correlation effects between the dipolar interaction of 13 C with adjacent protons and the interaction of the magnetic moment of 13 C with the anisotropic electronic shielding. The solutions of Redfield equations have been used for the interpretation of the time evolution of the 13 C multiplet spectral lines. The autocorrelation terms of the relaxation matrix have been calculated from contributions to the proton relaxation and the relaxation rate of 13 C during proton decoupling. Cross-correlation terms and cross-correlation times for methylene 13 C have been calculated from initial slopes of experimental relaxation curves, and defined more precisely by their theoretical adjustment. The correlation times indicate that the rotation of the ethanol methylene group is anisotropic.