Rearrangement of phenylcarbene radical cation to dehydrotropylium cation

Dichlorocarbene radical cation reacts with benzaldehyde in the gas phase by oxygen radical anion abstraction, generating a new carbene radical cation population. The ion population consists of two isomeric carbene radical cations. Molecular orbital calculations, diagnostic ion-molecule reactions, and examination of ion-molecule reactions' kinetics and thermochemistry were utilized to elucidate the structures (phenylcarbene radical cation and dehydrotropylium cation), provide the relative abundances (20% and 80%, respectively) and propose a likely mechanism for the formation of the two isomeric carbene radical cations. A single potential energy surface was found to explain the formation of both carbene radical cations. Oxygen radical anion abstraction followed by prompt dissociation of the collision complex leads to the formation of the phenylcarbene radical cation. However, in a longer-lived collision complex, the phenylcarbene radical cation can rearrange to a more stable isomer, the dehydrotropylium cation.