Gas-Phase NMR Studies of N,N-Dimethylthioamides. Influence of the Thiocarbonyl Substituent on the Internal Rotation Activation Energies

Temperature-dependent gas-phase ¹H NMR spectra of seven thiocarbonyl-substituted N,N-dimethylthioamides (YCSN(CH<INF>3</INF>)<INF>2</INF>) obtained at 300 MHz are consistent with the following free activation energies ΔG^&thermod;<INF>298</INF> (kcal mol^-1):  Y = H, 22.5 (0.1); CH<INF>3</INF>, 18.0 (0.1); F, 18.3 (0.1); Cl, 16.9 (0.2); CF<INF>3</INF>, 17.2 (0.1); CH<INF>2</INF>CH<INF>3</INF>, 17.6 (0.1); CH(CH<INF>3</INF>)<INF>2</INF>, 16.3 (0.1). The results are compared to condensed-phase values and to the corresponding gas-phase oxoamides.