GAS-PHASE BIOMOLECULAR CHEMISTRY OF THE BULLET-CHNC AND BULLET-CHCN RADICAL-ANIONS

The gas-phase ion/molecule chemistry of the .-CHNC and .-CHCN radical anions formed in the reactions of the O.- ion with CH3NC and CH3CN respectively, has been studied by Fourier transform ion cyclotron resonance mass spectrometry. The gas-phase acidity, DELTA-H-degrees(acid), of the .CH2NC radical is determined to be 1582 +/- 10 kJ mol-1, while the .CH2CN radical is considerably more acidic in the gas phase (DELTA-H-degrees(acid) = 1563 +/- 3 kJ mol-1). The .-CHNC ion does not react with the parent compound by proton abstraction in accordance with the gas-phase acidity of CH3NC, which is determined to be 1589 +/- 8 kJ mol-1 on the basis of a proton-transfer equilibrium between -CH2NC and CH3OH. The .-CHNC and .-CHCN radical anions react with HCO2CH2CH3, CF3CO2CH2CH3, CF3COSCH2CH3 and CH3SSCH3 to form product ions of the same type, but in significantly different abundance ratios. In particular, the reaction of the .-CHNC ion with HCO2CH2CH3 proceeds by loss of an ethoxy radical and an ethanol molecule from the collision complex, whereas the reaction of the .-CHCN ion with this substrate results almost exclusively in elimination of an ethoxy radical.