Ion–molecule reactions of [ketene]+˙ as a diagnostic probe for distinguishing isomeric alkenes,alkynes and dienes: A study of the C4H8 and C5H8 isomeric hydrocarbons

The gas-phase ion–molecular reactions of ketene]^+˙ with a number of isomeric alkenes, alkynes and dienes were studied by using tandem mass spectrometry. Ketene was reacted with C₄H₈ (but-1- and ?2-ene and 2-methylpropene) and C₅H₈ unsaturated hydrocarbons (isoprene, penta-1,3- and ?1,4-diene, pent-1- and ?2-yne, cyclopentene and methylenecyclobutane) in a high-pressure chemical ionization source of a tandem mass spectrometer. The collisionally stabilized ion–molecule adducts were analyzed by use of collisionally activated dissociation (CAD) spectra. The three C₄H₈ alkenes were distinguishable on the basis of the distinct CAD spectra of their adducts with ketene. Similarly, the CAD data for the corresponding adducts derived from the C₅H₈ hydrocarbons point to different structures for the C₅H₈ compounds.