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

This report discusses the validity of the one-to-one empirical relationship between the existence of an interatomic bonding interaction and a corresponding bond critical point bcp between two atoms within the molecular system. This relationship is known as Bader's rule and is supported by the Quantum Theory of Atoms in Molecules (QTAIM). This rule has been questioned for some molecular systems, despite exhibiting strong experimental evidence of intramolecular hydrogen-bond-like interactions (HBI). To carry out the discussion, we have chosen two molecular systems as cases of study: 1,2-ethanediol and 1,2-dihydroxybenzene (catechol), which follow the above conditions. In this way, these systems help us confirm the rule's validity for such weak interactions. The difficulty in detecting and determining the existence of a bcp associated with the interaction in these cases originates from the high planarity of the electronic density surface in the space between the oxygen and hydrogen atoms that define the bridge. We successfully relaxed certain criteria in standard search processes, allowing us to uncover critical points and gain a deeper understanding of this interaction. Our findings robustly support using the Bader-Popelier topological criterion for detecting 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.