Effect of protonation on the atomic and bond properties of the carbonyl group in aldehydes and ketones

Protonation in a series of aldehydes and ketones of formula R-1-CO-R-2 (wit h R-1, R-2 = H, Me, Et, Pr and Bu) was studied by using the theory of atoms in molecules to examine the atomic and bond properties of the carbonyl gro up and its relationship to the energy involved in the protonation process. Based on the results, aldehydes, methyl ketones and the remainder dialkylke tones studied exhibit three different behaviours. Protonation results in sm all differences in the properties of the C=O bond. While the atomic charge of the carbonyl group hardly changes, the proton bonded to the oxygen exhib its high positive charge after protonation. Atomic contributions to the tot al energy depend on molecular size. (C) 1999 Elsevier Science B.V. All righ ts reserved.