The conformational equilibrium of N,N'-bis[(S)-1-phenylethyl]-thiourea and its solvent dependence, studied by NMR and CD spectra and by X-ray crystallography

Favoured conformations of N,N'-bis[(S)-1-phenylethyl]thiourea (1) have been predicted by empirical force-field calculations, and the corresponding rotational strengths for the important transitions in the near UV region have been calculated. Experimental studies by 1H NMR, IR, UV, and CD spectroscopy have permitted the assignment of a conformation denoted E,Za to the conformer, which dominates in nonpolar solvents, while hydroxylic solvents were found to favour conformations of Z,Za type. The E,Za conformer is also predicted by force-field calculations to be the most stable one.Key words: circular dichroism, conformation, crystal structure, dynamic NMR spectroscopy, N,N'-bis[(S)-1-phenylethyl]thiourea.