Cyano-, nitro- and nitrosomethane derivatives: Structures and gas-phase acidities

The structures and gas-phase acidities of resonance-stabilized methane/methanide derivatives (H[(CRRR3)-R-1-R-2]/ [(CRRR3)-R-1-R-2](-) with R-1,R-2,R-3 = H, NO2, NO, and CN) have been studied through B3LYP/aug-cc-pvTZ computations. The gas-phase acidities lie in the range 1523-1459 for singly, 1365-1304 for doubly and 1274-1203 kJmol(-1) for triply substituted methane derivatives. In the NO-substituted methanides, protonation always occurs at the nitroso group, leading to the corresponding oxime. For the cyano- and nitromethane derivatives the C-H bonded isomer was found to be the more stable species. For mixed CN/NO2-substituted methanides, protonation of the nitro group is energetically favourable except for the simplest cyanonitromethanide in which protonation occurred at the central carbon. Significant resonance effects occur in all three classes of methanides (NO2-, NO- and CN-substituted). However, the magnitude of this effect differs significantly depending on the degree of substitution. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).