The photoelectron spectra of a series of ketone compounds have been investigated in the gas phase. Core ionization energies were measured to probe the effects of molecular size and connectivity number on core ionization energies. It was found that core ionization energies roughly decrease with increasing connectivity number as expected. However, subdividing into several categories based on the molecular type gives improved correlations. These results show both the effect of molecular size and that of bringing the polarizable group closer to the core ionized center. In some cases, compounds with the same connectivity number have different core ionization energies and, in others, compounds with different connectivity number have the same core ionization energies. These discrepancies indicate that the simple method for calculating connectivity numbers must be modified to reflect different molecular types. Other discrepancies indicate that this method does not correctly predict the effects of remote hydrogens or the effects of aromatic substituents, where conjugation may influence the relaxation energy. / Graduation date: 1995