Coupled relaxation in AX2 spin systems. Dependence of effective relaxation times on method of measurement and application to determining internuclear distances

Abstract

A simple treatment of relaxation in AX₂ all-proton systems shows that under certain conditions the effective spin-lattice relaxation time of the total A or X signal depends on the method of measurement. The calculations have been confirmed by measurements on 1,3-dinitro-2-chlorobenzene in CDCl₃ and 1,1,2-trichloroethane in CDCl₃, (CD₃)₂CO and C₆D₆. The experimental relaxation times, together with nuclear Overhauser enhancements, have been used to determine internuclear distances and rotational correlation times. There is good agreement with values of these parameters obtained from independent sources.