Theoretical study of the HCN-CH3 and HNC-CH3 radicals: Hydrogen and covalent bonding

The interaction between the methyl radical with hydrogen cyanide and hydrogen iso-cyanide is reported at several ab initio levels of theory. Four structures are studied: two hydrogen-bonded (H3C⋯HCN and H3C⋯HNC) and two covalent-bonded (H3C-NCH and H3C-CNH) structures. It is shown that hydrogen cyanide forms a weak hydrogen bond with the methyl radical (DeCP=−1.3kcal/mol), while its covalent-bonded isomer is mostly unbound with respect to the fragments ground state (DeCP=+0.5kcal/mol). The ground state of the hydrogen isocyanide complexed with the methyl radical is found to be a covalent-bonded complex (DeCP=−25.5kcal/mol), whereas its hydrogen-bonded isomer is only a weak complex (DeCP=−2.2kcal/mol).