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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.

Hydrogenation reaction of ethene on free Ir4 cluster was theoretically investigated using DFT B3LYP level of theory with LanL2Dz basis set. It was found that hydrogen molecule adsorption proceeded without an apparent transition state structure and the adsorption energy was predicted to be −93.7 kJ/mol. Two possible channel of hydrogenation reaction were investigated. Distortion of cluster frame and high values of activation energies make these channels unfavorable. It was shown that inclusion of magnesium oxide (MgO) support model in our calculations account for a considerable variation of geometric parameters of Ir4 cluster. The bonding of a single carbon ligand to the supported tetrahedral Ir4 cluster at the on-top site was also modeled to probe changes in geometric parameters in comparison with unsupported cluster. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011