HINDERED ROTATION IN N-METHYLTHIOUREA

A study of the barrier to rotation about the carbon-nitrogen bond in N-methylthiourea in pyridine, acetonitrile-d3, trifluoroacetic acid, methanol, water, and deuterium oxide was performed by the nmr technique. In these solvents it was observed that below 5° there were two methyl doublets of unequal intensity and coupling constants. The coupling constant of the high-field doublet was 0.5 Hz greater than that of the low-field doublet and was assigned to the trans isomer. From the ratio of the trans to cis areas equilibrium constants were calculated and were found to be solvent and temperature dependent. From the coalescence of the methyl doublets approximate activation energies were calculated and found to increase slightly as the polarity of the solvent increased.