Spectroscopic studies of model carbonyl compounds in CO2:: Evidence for cooperative C-H•••O interactions

Acetylated carbohydrates have extremely high solubilities and miscibilities in CO2 and form the basis of a new approach toward the development of renewable CO2-philes. Ab initio computational studies relevant to this system indicate that in CO2 complexes with simple, model carbonyl compounds the Lewis acid-Lewis base interaction between the carbon atom of CO2 and the carbonyl oxygen is accompanied by a cooperative, intermolecular C-H...O interaction between the CO2 oxygen and the solute's hydrogen atom. The results show that this may provide an additional stabilization mechanism for solvation complex formation. Spectroscopic studies provide the best approach to study these interactions and the validation of either computational or theoretical models. The present study focuses on room temperature, gaseous, liquid, and supercritical condition spectroscopic data to evaluate the extent that such complexes are relevant to CO2 solvation. An examination of the temperature- and density-dependent changes in the vibrational spectra and the NMR shielding constants in both interacting (CO2) and noninteracting (N-2 and He) systems supports the existence of the C-H...O interaction.