Carbon and oxygen 1s ionization energies of the carbonyl group of ketones

Carbon and oxygen Is ionization energies for the carbonyl group have been m easured in the gas phase for 18 ketones. The shifts in these measured ioniz ation energies, together with similar data for aldehydes from the literatur e, are compared with the predictions of electronic structure calculations b ased on the equivalent-cores model. It is found that the ab initio results using the 6-31G* basis set correlate linearly with the experimental results , but the slopes of the correlations are not 1. For oxygen the predicted sh ifts are 0.9 times the observed values and for carbon they are 1.3 times th ose observed. Oxygen Is ionization energy shifts calculated using the semi- empirical AML method also correlate well with the experimental values, but with a slope of only 0.54. For the carbon Is energies, the predictions of t he semi-empirical calculations correlate only with the data for the ketones (slope of 0.63) and fail noticeably for the aldehydes. (C) 1999 Elsevier S cience B.V. All rights reserved.