E Z Stereoisomerization in Methylene bis-Dithiocarbamate and N,N,S Trimethyldithiocarbamate
Rates of rotation about the carbon-nitrogen partial double bond in N,N,Strimethyldithiocarbamate (1) and methylene bis-dithiocarbamate (2) were measured by the dynamic NMR technique known as selective inversion recovery. Free energies of activation (AG*) for the rotational barrier about the carbon-nitrogen partial double bond in compounds 1 and 2 were determined in a variety of solvents. Compound 1 was found to have a lower rotational barrier than compound 2. As solvent polarity increased, an increase in rotational barrier was observed. Contrary to expectations, hydroxylic solvents lowered the rotational barrier for compounds 1 and 2 based on their increased solvent polarity and hydrogen bonding capabilities. These results have implications for determining switching rates in dithiocarbamate chiroptical switches.