Natural bond-bond polarizability: a Hückel-like electronic delocalization index

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• The bond-bond polarizability index, originally developed in Hückel theory, describes electron delocalization.
• Natural Bond Orbital (NBO) analysis provides insights into electronic structure and bonding.

Purpose of the Study:

• To generalize the bond-bond polarizability index within the Natural Bond Orbital (NBO) framework.
• To develop a quantitative descriptor for various electronic delocalization phenomena.

Main Methods:

• Generalization of the Coulson-Longuet-Higgins bond-bond polarizability index.
• Application within the Natural Bond Orbital (NBO) framework.
• Integration with ab initio molecular orbital and density functional theory (DFT) methods.

Main Results:

• The developed natural bond-bond polarizability (NBBP) index effectively quantifies delocalization.
• The NBBP index captures effects from strong π aromaticity to weak hyperconjugation.
• Applications demonstrated across saturated/unsaturated species, reactions, and hydrogen bonding.

Conclusions:

• The NBBP index offers a flexible and quantitative tool for analyzing electronic delocalization.
• This generalized index enhances understanding of bonding in diverse chemical systems.
• The NBBP index provides valuable insights into chemical reactivity and intermolecular interactions.