Relaxation and linewidths in some nuclear magnetic resonance spectra

Abstract
Measurements of linewidths in conventional high resolution spectra have been used to investigate mechanisms of nuclear relaxation in viscous solutions. The line widths for ABX and A 2 X 2 systems have been calculated by means of Redfield’s theory and assuming relaxation by a random magnetic field; these are tabulated. The linewidths for an ABX system relaxing through the dipolar coupling of nuclei A and B are also tabulated. The mechanism of relaxation of a variety of small molecules in viscous solutions was found to be an intermolecular process, but not to be due to a dipolar field (such as would arise from a nuclear or electron spin). The relative signs of certain coupling constants in ABX and A 2 X 2 systems, which cannot be determined by analysis of the spectrum, can be found from such measurements; this is demonstrated for vinyl n -butyl ether and 1,2-dibromotetrafluorobenzene.