Elusive Cyanoform: Computational Probing Its Stability and Reactivity with Accurate Ab Initio Methods.

Abstract

We have applied the CCSD(T)-F12a/cc-pVTZ-F12//CCSD(T)/cc-pVTZ level of theory to calculate energies for 22 reactions pertinent to the stability and reactivity of hardly isolable cyanoform (HC(CN)3). A number of exothermic processes has been indicated, especially the hydration. In the predicted mechanism for the gas-phase hydration of cyanoform, the H2O addition to the C≡N bond corresponds to a rate-limiting step, which is aided by an extra molecule of water. Also, for the cyanoform dihydrate (H2NC(OH)C(CN)CONH2) product, the experimentally identified compound, the more stable planar isomer exhibits intramolecular O-H···O═C (not N-H···O═C) H-bonding. Our calculated structures, binding energies, and NBO data for [HC(CN)3]n (n = 2,4) clusters suggest that the non-conventional C-H···N H-bonds contribute to their stability. Among the surveyed structures of the C≡N group incorporating products of reactions examined, the CCSD(T)/cc-pVTZ molecular parameters of cyanocarbons C2(CN)4, C2(CN)6, and C6(CN)6 can be regarded as the most accurate gas-phase values up-to-date.