Ab Initio Calculations on CO2 Binding to Carbonyl Groups

Abstract

Ab initio molecular orbital calculations were performed at the SCF and MP2 levels, using a 6-31G basis set, for complexes of CO2 with carbonyl compounds. The specific interaction between CO2 and the carbonyl oxygen can be described as a Lewis acid−base reaction. Two different geometries, one having C2v symmetry and the other having Cs symmetry, were studied. The Cs symmetry was found to yield stronger binding of the CO2 complexes. The degeneracy of the ν2 bending mode in free CO2 was lifted when the CO2 was bound. The calculated ν2 splittings at the SCF level, using a 6-31G basis set, were comparable to literature values determined by IR spectroscopy of CO2-impregnated polymers. When steric hindrance was present, the binding energy of CO2 to carbonyls was reduced, resulting in lower ν2 splittings. The interaction energy between benzene and CO2 was determined to be much lower than that associated with a carbonyl oxygen and CO2. The preference of CO2 for the carbonyl group over the benzene ring, along with ...