Hindered C–N bond rotation in triazinyl dithiocarbamates

The substituent and solvent effects on the rotation around a C–N amide bond were studied for a series of triazine dibenzylcarbamodithioates. The Gibbs free energies (ΔG^‡) were measured to be 16–18 kcal/mol in DMSO-d₆ and toluene-d₈ using variable-temperature nuclear magnetic resonance (VT-¹H NMR) spectroscopy. Density functional theory (DFT) calculations reproduced the experimental observations with various substituents, as well as solvents. From the detailed analysis of the DFT results, we found that the electron donating dibenzyl amine group increased the electron population on the triazinyl ring, which decreased the rotational barrier of the C–N bond in the dithiocarbamate group attached to the triazinyl ring. The higher electron population on the triazine moiety stabilizes the partial double bond character of the S–C bond, which competitively excludes the double bond character of the C–N bond. Therefore, the rotational dynamics of the C–N bond in dithiocarbamates can be a sensitive probe to small differences in the electron population of substituents on sulfur.