pi.-Donor relaxation in the oxygen 1s ionization of carbonyl compounds

Oxygen 1s and carbon 1s binding energies have been measured for a wide variety of compounds containing the carbonyl group. It is concluded that most of the oxygen 1s ionizations include a rather large amount of electronic relaxation corresponding to ..pi.. electron donation from the groups bonded to the carbonyl groups. The data are analyzed in two different ways to derive ..pi..-donor relaxation energies. The two resulting sets of relaxation energies are in fair agreement, and either set may be used to estimate the relative ..pi..-donor abilities of substituents.