CROSS-CORRELATION EFFECTS IN THE SPIN-LATTICE RELAXATION OF ETHANOL METHYLENE C-13

The spin-lattice relaxation of methyl and methylene C-13 and H-1 of et hanols CH(3)CH(2)0D and CD(3)CH(2)0D diluted with CD(3)CD(2)0D has bee n studied by the inversion-recovery method. Recovery of the proton spe ctral lines is described by a single exponential function with the sam e rate constant for all transitions. Intramolecular, intergroup and in termolecular contributions to the proton longitudinal relaxation have been determined using the concentration dependence of the relaxation r ate of diluted samples. Methylene C-13 spectral lines are recovered no n-exponentially with the different rates. This behaviour is caused by the interference or cross-correlation effects between the dipolar inte raction of(13)C With adjacent protons and the interaction of the magne tic moment of C-13 With the anisotropic electronic shielding. The solu tions of Redfield equations have been used for the interpretation of t he time evolution of the C-13 multiplet spectral lines. The autocorrel ation terms of the relaxation matrix have been calculated from contrib utions to the proton relaxation and the relaxation rate of C-13 during proton decoupling. Cross-correlation terms and cross-correlation time s for methylene C-13 have been calculated from initial slopes of exper imental relaxation curves, and defined more precisely by their theoret ical adjustment. The correlation times indicate that the rotation of t he ethanol methylene group is anisotropic.