Are Bond Critical Points Really Critical for Hydrogen Bonding?

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Physics

Background:

• Atoms in Molecules (AIM) theory is a standard method for analyzing chemical bonds, including hydrogen bonds.
• AIM theory's strict criteria can exclude systems exhibiting weak hydrogen bonds, leading to controversy.
• Existing methods focus on electron density critical points, which may not capture all relevant interactions.

Purpose of the Study:

• To investigate the limitations of Atoms in Molecules (AIM) theory in characterizing hydrogen bonds.
• To introduce and validate the Non-Covalent Interactions (NCI) index as a superior method for hydrogen bond analysis.
• To explore whether the general topology of electron density, not just critical points, defines hydrogen bonding.

Main Methods:

• Utilized the Non-Covalent Interactions (NCI) index for analyzing electron density.
• Applied a regional analysis of the reduced density gradient.
• Studied a series of 1,n-alkanediols to assess hydrogen bond formation.

Main Results:

• The NCI index provides a chemically intuitive description of hydrogen bonding in 1,n-alkanediols.
• Regional analysis of the reduced density gradient successfully identifies weak hydrogen bonds missed by AIM theory.
• The NCI approach generalizes the bond critical point analysis by considering the surrounding topological features.

Conclusions:

• The Non-Covalent Interactions (NCI) index offers a more comprehensive and chemically intuitive approach to hydrogen bond analysis.
• Hydrogen bond characterization should consider the general topology in the region of interaction, not solely electron density critical points.
• The NCI index transcends the limitations of AIM theory, providing a more robust assessment of hydrogen bonding.