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

TL;DR

This paper investigates cross-correlation effects in the NMR spectra of near-equivalent spin-1/2 pairs, revealing linewidth differences due to relaxation phenomena and developing a theoretical model that aligns with experimental data.

Contribution

It introduces a theoretical framework for cross-correlated relaxation in near-equivalent homonuclear spin-1/2 pairs with anisotropic diffusion, supported by experimental validation.

Findings

Inner peak linewidths differ significantly due to cross-correlation effects.

The developed theory accurately predicts experimental NMR lineshapes.

Strong anisotropic diffusion influences relaxation and spectral features.

Abstract

The NMR spectra of spin-1/2 pairs contains 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 13C2-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.