Proton cross relaxation effects in an AX 2 system

Abstract

Adiabatic rapid passage experiments on A and X resonances in the three proton (AX 2) system of 1,1,2-trichloroethane give single exponential decays with time constants 16.8 ± 1.0 sec and 7.2 ± 0.5 sec, respectively. These are interpreted as two time constants belonging to the total system which has characteristic two-exponential T 1 decays due to cross-relaxation effects. This interpretation was verified by performing two other experiments: (1) observation of the decay of total magnetization which shows a two-exponential character and (2) observation of changes in intensity of the A resonance while performing rapid passage on X nuclei which shows the presence of cross-relaxation. The results of all four experiments fall into a consistent pattern. The rate constants arising from dipolar interactions within each group and those between the two groups and the translational and rotational correlation times involved are determined.