Observation of cross correlations in a weakly coupled ¹⁹F-¹H four-spin system

Abstract

Cross correlation, an interference term between different relaxation pathways, manifests itself as a multiplet effect in coupled spin systems, which can be described in terms of longitudinal multispin orders. Experimental observation of these multispin orders is proof and a measure of the cross correlations. The cross correlations between the chemical-shift anisotropy (CSA) relaxation of fluorine and its dipolar relaxation with protons have been measured here in 1-fluoro-2,4-dinitrobenzene. It is found that this cross correlation is significant between the fluorine CSA and its dipolar relaxation to the proton ortho to it and is small but measurable to the other protons.