Effect of halogen substituents on C–N bond strength in nitromethane

Present theoretical study has been carried out with objective to reveal effect of chlorine and fluorine substituents on C–N bond strength in nitromethane. Gn, W1 and CBS-QB3 composite techniques were employed to compute accurate values of formation enthalpies of halogenated nitromethanes, corresponding radicals and ΔrH0(C–N) values. Calculations on DFT and ab initio levels were performed using B3LYP and QCISD methods. It was found that substitution of hydrogen by fluorine atoms causes only slightly decreasing of ΔrH0(C–N), whereas accumulation of chlorine atoms tends to decrease C–N bond strength significantly. Formation enthalpies of halogenated nitromethanes and corresponding radicals were calculated using both atomization approach and involving isodesmic reactions.