Gas-Phase Reactivity of Phenylcarbyne Anions

Gas-phase reactivities of the phenylcarbyne anion and its four derivatives were studied using a linear quadrupole iontrap mass spectrometer. The phenylcarbyne anions were calculated to have a triplet ground state (singlet-triplet splittings of 4-9kcal mol-1), with the exception of the 4-cyanophenylcarbyne anion that has a singlet ground state (singlet-triplet splitting of-1.9kcal mol-1). Only the phenylcarbyne anions with a triplet ground state react with acetone and dimethyl disulfide via radicalmechanisms. On the other hand, only the phenylcarbyne anion with a singlet ground state abstracts H2O and H2C???C???O fromacetic acid via electrophilic addition of the reagents to the anion. Finally, two hydroxy-substituted phenylcarbyne anions (with tripletground states) partially tautomerize with the assistance of reagent molecules to the more stable distonic phenylcarbene anions. Thisoccurs via abstraction of a proton from the reagent by the phenylcarbyne anion to generate a neutral (triplet) phenylcarbene and areagent anion, which is followed by proton abstraction from the hydroxyl group of the neutral phenylcarbene by the reagent anion togenerate the distonic phenylcarbene anion in an excited triplet state. Experiments performed on deuterated hydroxy-substitutedphenylcarbyne anions verified the mechanism. The reactivities of the distonic phenylcarbene anions were found to be quite differentfrom those of the phenylcarbyne anions. For example, they were found to abstract CH2from acetonitrile, which is initiated by C-Hinsertion???typical singlet carbene reactivity