A COMBINED MASS-SPECTROMETRIC AND THERMOCHEMICAL EXAMINATION OF THE C-2,H-2,N FAMILY OF CATIONS AND RADICALS

A detailed mass spectrometric and thermochemical investigation was made of the C-2,H-2,N family of radicals and cations. The following thermochemical data were obtained: Delta(f)H degrees(298)((CH2CN)-C-+) = 291 +/- 2 kcal mol(-1), Delta(f)H degrees(298)((CH2NC)-C-+) = 282-293 kcal mol(-1), Delta(f)H degrees(298)(HCCHN+) less than or equal to 272 kcal mol(-1), Delta(f)H degrees(298)((CH2CN)-C-.) = 58 +/- 3 kcal mol(-1), Delta(f)H degrees(298)((CH2NC)-C-.)= 96 +/- 3 kcal mol(-1), and Delta(f)H degrees(298)(HCCHN.) approximate to 81 kcal mol(-1). Mass spectrometry showed that the precursor molecules CH3CN, CH3NC, and 1-H-1,2,3-triazole all produce the lowest energy cyclic ion upon dissociative ionization. The linear (CH2CN)-C-+ ion could only be made from ICH2CN, a situation similar to the isoelectronic C-3,H3+ isomers. The above thermochemistry was used to explore pi-delocalization in the linear cations and radicals. Only (CH2CN)-C-. exhibits delocalization of the radical center while delocalization of charge occurs in both linear cations.