The relative singlet-triplet separations of five simple species of general formula R-NO, has been estimated by GVE3 calculations with bc;th double-zeta and polarized doublezeta basis sets. Electronegative substituents raise the calculated singlet-triplet separation. Qualitative aspects of these substitucnt effects are discussed. 1. lntroduc tion The electronic structure of species of general for-I mula R-NO2 has been of considerable interest recently, in part because of the vast thermo-and photorchemistry of these compounds [l] and in part because of the unusual nature of the ground electronic states of these systems. Briefly, the ground state ofnitromethane (and all other simple nitro derivatives) re: quires a multideterminant wavefunction for a proper description. Th+ he-been noted by a number of authors [24] _ We have also recently shown [3] that nitrornethane is actuay predicted to be a ground state ~~-$.?et at the single determinant RHF level with a minimum basis set, and that reasonable values of the singlet-triplet bparation require both a fairly large basis set and significant amounts df electron correlation. The multiconfigurational character of the ground state of these systems may be traced to the small HOMOLLUMO1gap; which arises from the-orb&& of local R symmetry on the NO2 group. _ The Hartree-Fockconfiguration-is _-_-* Re&&h spons&~ by thk%okrt~A Welch _F&&latioi