I. Wawer, R. Anulewicz-Ostrowska,, D. Maciejewska
2000
Citations
0
Influential Citations
3
Citations
Journal
Polish Journal of Chemistry
Abstract
Several N 1 N 2 -diaryl and N 1 -alkyl-N 2 -arylthioureas were examined earlier [1–6] by 1 H NMR in different solvents at various temperatures in order to establish rotational barriers around the C–N bond and conformational stability. The N 1 N 2 -disubstituted thioureas can exist in solution as an equilibrium mixture of three conformers EZ, ZE and EE, because the fourth conformer ZZ (with voluminous substituents at the same side of the C=S group) is unstable due to the steric hindrance. Interesting model compounds for the study of structural effects are the N-phenyl thioureas with ortho hydroxyl substituent to the phenyl ring, because OH and NH proton-donor groups can be involved in different intra and/or intermolecular hydrogen bonding. In our studies on substituted thioureas four compounds have been synthesized with methyl or propene (allyl) substituent at N 1 and with 4-methyl or 5-methyl group in addition to 2-hydroxyl at aromatic ring at N 2 (see Figure 1). In order to estimate the favoured conformation in the solid state, as well as to rationalize the results of IR and solid state NMR, we determined the structures of the two N 1 -methyl thioureas by X-ray diffraction (XRD). Cambridge Structural Database contains numerous N-phenyl ureas but only eight N-phenyl thioureas. The few data only for thioureas can be understood by known difficulties in collecting reflexes from sulphur atoms (high scattering factor