Cooperative C−H···O Hydrogen Bonding in CO2−Lewis Base Complexes: Implications for Solvation in Supercritical CO2

Abstract

Understanding the fundamental principles for the design of CO₂-philic materials is of growing importance due to the potential for enabling “green” chemistry and technologies in liquid and supercritical CO₂ as alternative solvent systems. Recently, there have been numerous efforts to develop hydrocarbon-based CO₂-philes containing carbonyl groups, which are known to interact through a Lewis acid−Lewis base (LA−LB) interaction with CO₂ molecules, thereby providing the necessary solvation energy for dissolution. In this work, we investigate the role of a weaker, but cooperative, C−H···O hydrogen bond as an additional stabilizing interaction in the solvation of polycarbonyl moieties with hydrogen atoms attached directly to the carbonyl carbon or to the α-carbon atom. Ab initio calculations are performed on simple intermolecular complexes of CO₂ with compounds capable of acting as Lewis bases. Systems studied in different interaction configurations include formaldehyde, acetaldehyde, acetic acid, and methyl acetate, as model carbonyl compounds, and dimethyl sulfoxide as a model system for the sulfonyl group. Interaction energies, vibrational frequencies, charge transfer, and other molecular properties are calculated. Results indicate that C−H···O hydrogen bonds may be an important stabilizing interaction that merits consideration in the design of future CO₂-philes.