Relative energies of C2O2H2 isomers and their ionized counterparts: possibility of bond stretch isomerism

Hybrid density functional theory and post-SCF ab initio calculations were employed to explore the isomers of glyoxal, C2O2H2, along with the corresponding cation and anion radicals. The dependence of relative energies with respect to the methods and quality of basis set was critically analyzed, all the way up to cc-pV5Z. Bond stretch isomerism between 5a and 6 as well as 5C and 6C was clearly established. While the glyoxal isomer 1 and 1A is a global minima on neutral and anionic surfaces, 8C a ketene analog was found to be the global minima among the cation isomers.