Conformational isomerism of chlorophenylthioureas and intramolecular N---H … Cl hydrogen bonds: IR spectra of N---H stretching vibrations

The vN---H regions of the IR spectra of thioureas with chlorophenyl (ClPh) groups and those with halophenyl groups were measured in dilute CCl₄ solution. The observed vN---H bands were classified into eight groups according to the wavenumbers and the two substituent groups. The suggested conformational states and the formation of intramolecular N---H … Cl hydrogen bonds in these compounds were discussed in comparison with those of the urea analogs. It was found that these thiourea derivatives are more stable in the cis form than the urea analogs and that thioureas with o-ClPh groups form fewer intramolecular N---H … Cl hydrogen bonds than do the urea analogs.