Density Functional Theory and Quantum Theory of Atoms in Molecules Analysis: Influence of Intramolecular Interactions on Pirouetting Movement in Tetraalkylsuccinamide[2]rotaxanes

Abstract

The first Quantum Theory of Atoms in Molecules (QTAIM) analysis of [2]rotaxanes was used in combination with quantum mechanical calculations and variable temperature NMR experiments. The study shows all the intramolecular interactions of tetraalkylsuccinamide[2]rotaxanes with different templates. The threads have different stoppers [R1R2NC(O)-CH2CH2-C(O)NR2R1, in which R2/R1 = CH2cy-Hex/CH2Ph, i-Bu, Bu, and Pr]. The different threads used allowed us verify that the contact area between the submolecular components (CMcy···Thr) is closely correlated with the interaction energy (GMcy···Thr) in the [2]rotaxanes studied. Furthermore, the QTAIM data and quantum mechanical calculations confirmed that, in all of the compounds, the hydrogen bonds are responsible for most of the energy from the intramolecular interactions that follow the C–H···π and H···H interactions, independent of the thread used. In the liquid state, using NMR 1H some intramolecular interactions were observed, which is in agreement with the data obtained in the solid state, thus making possible a comparison between the energy data obtained via the quantum mechanical calculations and the molecular movements of the [2]rotaxanes in solution. Consequently, a new way of understanding the intramolecular interactions in [2]rotaxanes and the influence they have on the movement of molecular machines is presented.