Inter- and Intra-Molecular Interactions by Quantum Theory of Atoms in Molecule

In this exclusive chapter, we present a brief overview of the quantum theory of atoms in molecule (QTAIM) proposed by R. F. W. Bader. This theory is based on the topological analysis of the electron density and related parameters. One of the strengths of this theory is the accurate prediction, characterization, and quantification of various interactions, including H-bond and van der Waals interactions. Herein, we discuss the important aspects of QTAIM regarding the intra- and intermolecular interactions in biologically active molecules discussed in the preceding chapters. Within the framework of the QTAIM, I mention the criteria of H-bonds and characterize the various H-bonds on the basis of topological parameters, and continue to quantify the strength of the H-bond. I will also describe a very user-friendly software AIMAll to perform the QTAIM analysis and explain the obtained results. In order to provide the contents digestive, I will include examples of molecules from Chapters 3, 4, and 5. I believe that this chapter will guide the readers interested in various kinds of interactions in biologically active molecules.

Keywords: AIM, AIMAll, BCP, Bond strength, BSSE, Characterization, Complex, Counterpoise, Dimer, Electron density, H-bond, Intermolecular interaction, Intramolecular interaction, Laplacian, Molecular graph, QTAIM, RCP, Reactivity, Stabilization, Supermolecular approach, Topology.