A theoretical investigation into the conformational changes of dibenzo- p-dioxin, thianthrene, and selenanthrene

Abstract

Theoretical ab initio calculations using the HF and B3LYP methods have been carried out to investigate the conformational differences of three cyclic rings, dibenzo- p-dioxin (DPD), thianthrene (THT), and selenanthrene (SET). The physical origin for the conformational preference of each molecule has been studied using the natural bond orbital (NBO) analysis. The NBO results indicate that DPD exists in a planar form due to strong electron delocalization caused by the specific orbital interaction, n π → π CC ∗, around the X atom. On the other hand, THT and SET exist as puckered forms with high inversion barriers due to less effective electron delocalization. The NBO analysis also shows that the conformational stabilization in DPD is caused by a more effective overlap of the 2 p z – π CC ∗ orbitals, compared with the overlap of the 3 p z – π CC ∗ orbitals in THT.