A theoretical study of the addition reactions of HF, H2O, H2S, NH3 and HCNto carbodiimide and related heterocumulenes

Using ab initio methods at different levels of theory (RHF/6-3IG*, B3LYP/6- 311G** and MP2/6-311 ++ G**), we have investigated the reaction mechanism i n gas phase of the addition of one molecule of HF, H2O, H2S, NH3, and HCN t o carbodiimide, carbon dioxide and ketene. In this last case both modes of addition were studied, i.e. across the carbon-carbon and the carbon-oxygen double bond. The potential energy surfaces were explored and the stationary points representing the reactants, transition states and products were loc alized. In all cases, the bond order and electron densities at the bond cri tical points were evaluated. Although our results correspond in all cases t o large energy barriers for the 1:1 addition processes, these barriers are related to the results obtained using several molecules of water or ammonia . (C) 2001 Elsevier Science B.V. All rights reserved.