Ab initio conformational study of vinylogues. 2-butene, stilbene and their conjugated polyenes

A conformational study of two vinylogue series: 2-butene, stilbene and their conjugated polyenes was carried out. In this study ab initio (RHF/3-21G and RHF/6-31G(d)) and Density Functional Theory (B3LYP/6-31G(d)) calculations were performed. Our results indicate that RHF/3-21G calculations are sufficient to use in preliminary form. However, it is prudent to use this technique only for a preliminary or exploratory conformational analysis. Thus, more accurate calculations with the inclusion of electron correlation appear to be necessary to confirm critical points at the Potential Energy Hypersurface of these compounds. In the present paper we report a complete and comprehensive picture of the conformational intricacies of the vinylogues with a small conjugated connecting chain (n=2-8). In addition an 'educated guess' for the conformational behaviour of large-size vinylogues is also reported. (c) 2005 Elsevier B.V. All rights reserved.