Intramolecular π–π Interactions in Diethanodihydronaphthalene and Derivatives: Dynamic and Static Behavior of the Interactions Elucidated by QTAIM Dual Functional Analysis

Abstract

AbstractDynamic and static behavior of the intramolecular π–π interactions between ethylene moieties in diethanodihydronaphthalene (1 a) and the derivatives (2 a–12 a) are elucidated by employing QTAIM‐DFA (QTAIM dual functional analysis), which we proposed recently. Total electron energy densities Hb(rc) are plotted versus Hb(rc) – Vb(rc)/2 at bond critical points (BCPs) for the interactions in question in QTAIM‐DFA, where Vb(rc) are potential energy densities at BCPs. After analysis of the plots, the π–π interactions in 1 a–12 a are all classified by the pure closed shell interactions and characterized to have the vdW nature with MP2/6‐311G(d), except for those in 10 a–12 a, where the ethylene moieties in 1 a are replaced by benzene moieties. The character in 10 a–12 a is predicted to have the typical‐HB (hydrogen bond) nature without covalency, although that in 10 a and 11 a seems close to the border area between the two. Indeed, the twisted structures were predicted for 1 a–4 a with MP2/6‐311G(d), but the observed non‐twisted structures of 1 a–3 a were better reproduced with MP2/6‐311G(3d). The typical‐HB nature without covalency was additionally predicted for the interactions between ethylene and benzene moieties in 9 a with MP2/6‐311G(3d), maybe due to somewhat shorter distances predicted for the interactions in question. The interaction in TS is also discussed exemplified by 10 a (C2v).