Resonance Response to Intermolecular Interaction: A Natural Resonance Theory Analysis

Although the concept of resonance is a key element of any organic chemistry course, its modulation by supramolecular stabilization remains poorly explored. This article seeks to address this issue with the use of natural resonance theory and other computational tools such as ab initio methods (DF-MP2, coupled-cluster singles and doubles, and SAPT2 + 3(CCD)δ_MP2), interaction region indicator, and charge-transfer analysis. A set of structurally straightforward noncovalently bonded systems with general formula X/H₂O where X = CO₂, SO₂, HCONH₂, C₄H₄O, and C₆H₅NH₂ is subjected to investigation. The findings indicate that the complexation can have significant impact on the relative weights of the resonance structures observed for isolated X by up to 32%. Furthermore, formation of X/H₂O complex is found to introduce new resonance structures with water's outer-valence electrons participating in the resonance. These findings broaden understanding of how supramolecular interactions shape resonance, a fundamental concept in chemistry, and can improve predictions of molecular behavior in complex systems.