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

Ágúst Kvaran*,  Ásgeir E. Konrádsson, Christopher Evansa) and Jón K.F. Geirsson
Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland.

a) Current Address: Department of Chemistry, Biology and Chemical Engineering, Ryerson Polytechnic University, 350 Victoria St., Toronto, ON, Canada, M5B-2K3


1H 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 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 nearby C-Cl bonds. Both ethylene and some ring proton chemical shifts are found to be dependent on ring current effects, which are substituent and ring orientation dependent. UV spectra support the structural predictions based on the molecular mechanic vs. NMR correlation analysis. Average minimum energy conformations of compounds1 - 10 are given in the paper.