Structure and electronic properties of the nitromethyl anion, nitromethane and aci-nitromethane

Abstract

Ab initio SCF MO calculations of the minimal and double-zeta level have been made for nitromethane, its aci tautomers and for planar and pyramidal forms of the nitromethyl anion. Calculations at the double-zeta level suggest that the most stable form of the ion is planar or near planar. Potential energy contours for the ion show that the planar form is expected to protonate on the oxygen (the observed fast reaction) whereas the pyramidal form would protonate on the carbon. This conclusion is not obvious by a comparison of the net atom charges alone. The p.e. spectrum of nitromethane has been re-assigned on the basis of our calculations; the first p.e. band is due to π ionization and the second is a combination of the two oxygen lone-pair ionizations.