Carbon Dioxide Stability and C═O π-Bond Strengths

π-Bond energies for a series of C═O containing compounds including carbon dioxide are determined using G3 and W1 calculations. These two computational methods give results that are in good accord, and in the latter case span a 37 kcal mol^-1 range from 75 (CH₂═O) to 112 (CO₂) kcal mol^-1. This sensitivity to substituent effects on the π-bond strength is attributed to Coulombic interactions between the oppositely charged carbon and oxygen atoms in the carbon-oxygen double bond. In contrast, carbon-carbon π-bond energies of a related series of compounds are found to be relatively constant (i.e., the variation is only 3 kcal mol^-1). The C═O π-bond strengths are also found to linearly correlate with the atomic charge at carbon as well as heats of hydration and hydrogenation.