CONFORMATIONAL ANALYSIS OF 3-AMINOTHIACYCLOHEXANE AND DERIVATIVES BY LOW-TEMPERATURE 13C NMR

Article abstract of DOI:10.1016/S0040-4020(01)86740-5

Several gauche interactions between sulfur and nitrogen functions are determined from measurement of conformational equilibria of 3-(X)-thiacyclohexanes (X = NH2, NMe2 NHPh and NHCO2t-Bu), their epimeric sulfoxides, and the corresponding sulfones, by low-temperature carbon-13 and proton NMR spectroscopy.The (RNH/S)gauche interaction is 0.18 (R = H), -0.04 (R = Ph) and -0.31 (R = CO2t-Bu) kcal/mol.The (Me2N/S)gauche interaction is 0.70 kcal/mol, of which 0.26 kcal/mol is estimated to arise from the gauche repulsive effect between the electron lone pairs.The (RNH/SOx)gauche interactions in the in the trans-sulfoxides (x=1) are approximately as destabilizing as expected on simple steric grounds, whereas in their cis epimers and in the sulfones they are 0.65 (R=H, x=1), 0.28 (R=H, x=2), -0.78 (R=Ph, x=1), -0.22 (R=Ph, x=2), < -1.94 (R=CO2t-Bu, x=1) and < -1.41 (R=CO2t-Bu, x=2) kcal/mol.Concentration and solvent effects in RNH- series are small, intermediate and large, respectively, when R is H, Ph or CO2tBu.The effect of protonation upon conformational equilibria is also discussed.