Nuclear Magnetic Double-Resonance Spectrum of a Strongly Coupled Two-Spin System

Abstract

The density-matrix theory of double resonance is applied for a detailed analysis of the frequency-sweep nuclear magnetic double-resonance spectra of the strongly coupled two-proton system in 2-bromo-5-chlorothiophene under various conditions of irradiation. These spectra show significant relaxation and coherence effects. The results of the theory are very sensitive to the relaxation mechanisms assumed for the system, indicating the possibility of deriving significant information about the relaxation of the system by this method. Comparison of the observed and theoretical double-resonance spectra shows that the proton relaxation in this molecule is due, in large measure, to external interactions with a high degree of correlation between the interactions with the two protons. An approximation proposed by Bloch for simplifying the calculations is found to be applicable even when the irradiation frequency is close to some single-resonance transition frequencies.