1H NMR and UV-Vis spectroscopy of chlorine substituted stilbenes:: Conformational studies

H-1 NMR and UV-Vis spectroscopic studies as well as molecular mechanics calculations have been performed for the trans and cis isomers of a series of chlorine substituted stilbenes (2-10). Correlations are found between the predicted molecular conformations and various NMR and UV-Vis spectroscopic parameters, indicating that these are suitable for conformational studies. The ethylene proton chemical shifts, in particular, are found to be sensitive to anisotropy effects of the nearby C-Cl bonds. Both ethylene and some ring proton chemical shifts are found to be dependent on the ring current effects, which are and ring orientation dependent. UV spectra support the structural predictions based on the molecular mechanic vs. NMR correlation analysis. Average minimum energy conformations of compounds 1-10 are given in the paper. (C) 2000 Elsevier Science B.V. All rights reserved.