Solvation of Amides in DMSO and CDCl 3 : An Attempt at Quantitative DFT-Based Interpretation of 1 H and 13 C NMR Chemical Shifts.

The study concerns N-methyl-2-pyrrolidinone, N,N-dimethylformamide, 2-pyrrolidinone, N-methylformamide, and formamide in DMSO-d6 and CDCl3 solutions. It has been shown that the results of DFT calculations [B3LYP and/or PBE0 6-311++G(2d,p), PCM] of molecular geometries and magnetic shielding are able to reproduce very well the amide 1 H NMR and 13 C NMR chemical shifts measured in these solvents provided that the specific solvation of the solute molecules and their association are taken into account and also that comparison of the experimental and theoretical data is carefully done. Analysis of the chemical shift data points out that in CDCl3 solutions primary and secondary amides are partially associated and that their carbonyl oxygen lone electron pairs are specifically solvated by solvent molecules. At the same time, association of the amides seems to be of minor importance in DMSO, while their N-H hydrogens form strong hydrogen bonds with solvent molecules.