Cross-correlation effects in the solution NMR spectra of near-equivalent spin-1/2 pairs

The nuclear magnetic resonance (NMR) spectra of spin-1/2 pairs contain four peaks, with two inner peaks much stronger than the outer peaks in the near-equivalence regime. We have observed that the strong inner peaks have significantly different linewidths when measurements were performed on a C-13(2)-labelled triyne derivative. This linewidth difference may be attributed to strong cross-correlation effects. We develop the theory of cross-correlated relaxation in the case of near-equivalent homonuclear spin-1/2 pairs, in the case of a molecule exhibiting strongly anisotropic rotational diffusion. Good agreement is found with the experimental NMR lineshapes. (C) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/).

Automated summary

In this study, the NMR spectra of spin-1/2 pairs in the near-equivalence regime were observed to have four peaks, with the two inner peaks stronger than the outer peaks. The strong inner peaks were found to have significantly different linewidths, potentially due to strong cross-correlation effects. The developed theory of cross-correlated relaxation in the case of near-equivalent homonuclear spin-1/2 pairs with strongly anisotropic rotational diffusion showed good agreement with experimental NMR lineshapes.