Conformational study of internally retrograde and quasi-retrograde molecules — An ab initio and DFT study

Abstract

A conformational study of the symmetrical and nonsymmetrical homologue series 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. The presence of two symmetrical aromatic systems (identical or not) reduces notably the conformational possibilities of these compounds. Our results indicate that RHF/3-21G calculations are sufficient to use in a preliminary form. However, from our results it is prudent to use this technique only for a preliminary or exploratory conformational analysis. Thus, at least, the HF level of theory in conjunction with more extended basis sets and the inclusion of electron correlation appear to be necessary to confirm critical points at the potential energy hyper surfaces (PEHSs) and to assign the conformational preferences of these compounds. In the present paper, we report a complete and comprehensive picture of the conformational intricacies of the compounds with a small flexible connecting chain (n = 1–5). In addition, an "educated guess" for the conformational behaviour of large-size homologues (n = 6–10) is also reported.Key words: ab initio and DFT calculations, conformational study, homologue series.