Isolated spin-pair analysis of 13C NMR relaxation rates in liquids

•Carbon-13 NMR relaxation rates are estimated by spin-pair analysis.•Force-field molecular dynamics simulations are useful to predict dipolar relaxation rates.•Optimal trajectory length depends on molecular conformational freedom.•Isolated spin-pair analysis reflects the molecular movement. In small organic molecules, dipolar relaxation rate R1DD is the most important mechanism for 13C NMR spin relaxation. Herein, the R1DD was used to analyze force-field molecular dynamics trajectories, corresponding to some neat liquids and solutions, in order to simulate 13C relaxation. The results show a satisfactory correlation between simulated and experimental values, structure-dependent behavior and self-diffusion effects due to differences in inertia axes that could be observed by the isolated spin-pair approach that avoids the solution of relaxation matrices, which helps in interpreting 13C relaxation experimental data from a molecular dynamics approach. [Display omitted]