Raman Spectroscopic Evidence for Cooperative C−H···O Interactions in the Acetaldehyde−CO2 Complex

Abstract
In carbonyl compounds having a hydrogen atom attached to the α-carbon or directly to the carbonyl carbon, our recent ab initio and solvation studies have predicted the presence of a weak C−H···O interaction with CO2. This intermolecular interaction acts cooperatively with the Lewis acid−Lewis base interaction that exists between CO2 and the carbonyl group. This communication provides the first experimental evidence for this cooperative interaction in the acetaldehyde−CO2 complex using Raman spectroscopy at 25.0 °C in the gas phase. The implications of these interactions in the solvation of carbonyl-based CO2-philes are also discussed.