Theoretical analysis of the influence of C–H⋯O bonds on the NMR constants of uracil in DMSO

We combined different models of solvation and density functional theory calculations to study the magnetic properties of uracil in the liquid dimethyl sulfoxide environment. Special attention was paid to the effect of weak hydrogen bonds formation. In uracil, C=O groups act as hydrogen acceptors while N–H is hydrogen donor. The influence in the intramolecular coupling involving the acceptor and donor sites in uracil is perceptible. The 1 J (C,O) and 1 J (N,H) coupling constants decrease by ca. 1.5 Hz and 2.3 Hz, respectively. This behavior depends on the nature of the hydrogen-bonding interaction and cannot be neglected. The best agreement between theory and experiment for the magnetic shielding was obtained using long-range or dispersion corrected exchange-correlation functional such as LC-BLYP, B97D, and ω B97XD. In the particular case of uracil, we concluded that the most important contribution to the calculated magnetic shielding for C–H ⋯ O interactions comes from electrostatic contributions.