Thiourea and isothiocyanate – two useful chromophores for stereochemical studies. A comparison of experiment and computation

Abstract

Thioureas and isothiocyanates, compounds of high importance in organic synthesis, have not been considered so far as chiroptical probes that can provide structural information from the analysis of circular dichroism spectra. CD spectra of a set of molecules containing the thiourea, isothiocyanate and phthalimide chromophores were obtained and analyzed on the grounds of the calculated populations of conformers and their individual contributions to the CD spectra. It is shown that the thiourea and isothiocyanate chromophores can provide useful structural information from the analysis of their exciton-coupled CD spectra. Exciton-coupled CD spectra of thioureas were found to be sensitive to the Z/E conformation of the chromophore. DFT calculations based on the B2LYP functional were shown to provide a better match with the experimental spectra collected in the short wavelength region, compared to the traditionally used B3LYP functional.