Gas-Phase Derivatization for Determination of the Structures of C₃H₅⁺Ions

The structure of the C₃H₅⁺ ions formed via halide atom loss from ionized allyl, cyclopropyl, and 1- and 2-propenyl halides was investigated by derivatizing the ions with neutral benzene and substituted benzenes to produce gas-phase adduct ions. The structures of pressure stabilized adduct ions were directly determined by obtaining their collision-induced decomposition spectra and comparing them with the CID spectra of model ions. Two C₃H₅⁺ ion structures were found to be stable, the allyl cation from cyclopropyl and allyl halides and the 2-propenyl cation from 2-propenyl halides. The C₃H₅⁺ ions from 1-propenyl halides exist as a 2:1 mixture of the two ion structures. The mechanism of reaction was shown to be electrophilic attack on the ring π system to produce a Wheland intermediate or other structure with the proton relocated. The reaction pathway was confirmed by Fourier transform mass spectrometry, and rate constants for the derivatization reaction were determined by using pulsed ICR.