Four N,N -dialkyldithiocarbamate esters have been prepared and examined by nuclear magnetic resonance. From the temperature variation of the N-alkyl resonances, estimates of the barriers to rotation about the C—N bond have been made. Activation energies of the order 10 to 12 kcal provide evidence for an appreciable amount of C—N double bonding; this lends support to the assignment of the "thioureide" band in present and earlier infrared studies.