Chapter 17 - Applications of the quantum theory of atoms in molecules and the interacting quantum atoms methods to the study of hydrogen bonds

Abstract

Hydrogen bonds are noncovalent interactions of paramount importance throughout physics, chemistry, and biology. Therefore, there have been numerous efforts to understand its most basic nature as well as its most intricate features. Herein, we focus on the insight provided on this interaction by two state-of-the-art methods for wave function analyses, that is, the Quantum Theory of Atoms in Molecules (QTAIM) and the energy partition yielded by the Interacting Quantum Atoms (IQA) approaches. First, we briefly survey these relevant tools in the field of Quantum Chemical Topology (QCT) emphasizing the most important characteristics of these methods for the study of hydrogen bonds. Later, we consider the essential chemical nature of hydrogen bonds as revealed by IQA and QTAIM. The perspective provided by other methods in the realm of QCT, such as that provided by the Non-Covalent Index method is also considered. Afterwards, we address σ and π cooperativity and anticooperativity of H-bonds. We also consider the importance of nonadditivity in different systems and processes like the bifunctional activity of water clusters in hydrolysis reactions, the solvation of charged species in water as well as resonance-assisted and -inhibited hydrogen bonds. We also present an overview of hydrogen bonds occurring in excited states, for example, those involved in excited state proton transfers and in archetypical systems like H2O clusters. Finally, we considered doubly and triply hydrogen-bonded systems which have been widely exploited in the areas of molecular recognition and supramolecular chemistry. Although this chapter is not all-inclusive monograph of the applications of QCT in the study of hydrogen bonding, we hope it presents clear directions for further progress in this exciting field.