Studies on Optically Active Amino Acids. XIX. Solvent Effects on Optical Rotatory Dispersion and Circular Dichroism of N-Dithiocarbethoxy-L-a-amino Acids

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Optical rotatory dispersion and circular dichroism curves of twenty N-dithiocarbethoxy-L-α-amino acids were measured in water, methanol, dioxane, chloroform, and benzene. Striking solvent effects on Cotton effect curves, due to n→π* transition of the >N-CSS chromophore, were found. The Cotton effect was inverted by changing solvents. These solvent effects were classified in five groups based on the chemical structure of their amino acids.
Cyclohexylammonium salts of these dithiocarbamates produced different solvent effects on Cotton effect curves due to the same transition of the >N-CSS chromophore.
The most reliable conditions for correlating the absolute configuration of a-amino acids to the sign of Cotton effect curves using dithiocarbamate derivatives were discussed.