Weak Interactions in Molecules: A Quasi-Coalescence Intramolecular Hydrogen Bonding Interactions Family Revisited

Abstract

This report discusses the validity of the one-to-oneempirical relationship between the existence of an interatomic bondinginteraction and a corresponding bond critical point bcp between twoatoms within the molecular system. This relationship is known asBader’s rule and is supported by the Quantum Theory of Atoms inMolecules (QTAIM). This rule has been questioned for some molecularsystems, despite exhibiting strong experimental evidence of intramolecularhydrogen-bond-like interactions (HBI). To carry out thediscussion, we have chosen two molecular systems as cases of study: 1,2-ethanediol and 1,2-dihydroxybenzene (catechol), which follow theabove conditions. In this way, these systems help us confirm the rule’svalidity for such weak interactions. The difficulty in detecting anddetermining the existence of a bcp associated with the interaction inthese cases originates from the high planarity of the electronic density surface in the space between the oxygen and hydrogen atomsthat define the bridge. We successfully relaxed certain criteria in standard search processes, allowing us to uncover critical points andgain a deeper understanding of this interaction. Our findings robustly support using the Bader−Popelier topological criterion fordetecting these weak chemical interactions, challenging previously reported conclusions. We also report the relevant integrated chemical magnitudes that define complex bonding patterns to complement the description.