Studies on Structures and Fragmentation Pathways of [C₆H₅O]⁺ Isomers in the Gas Phase by Mass Spectrometry and MO Method

Abstract

The value of kinetic energy released (KER) in the reaction [C₆H₅O] [C₅H₅] ⁺ CO for anisole and nitrobenzene is different from that for m- or p-substituted phenols. Collisionally activated dissociation (CAD) spectra of [C₂H_SO]⁺ isomers are classified into two groups: Anisole and nitrobenzene again differ from others. Mass spectral studies predict the existence of at least two [C₆H₅O]+ isomers in the gas phase both for metastable (decomposing) and stable (nondecomposing) ions.
A comprehensive treatm ent including the MO calculations by MINDO/3 of structures of these [C₂H₂O] ions has been done to estimate structures and their heats of formation.
The oxocyclohexadienyl cation for both anisole and nitrobenzene, and [CH2=C=CHCH=CHC=O]⁺ for substituted phenols are shown to be metastable ions. The cyc lopentadienecarbonyl cation is regarded as stable ions for anisole and nitrobenzene, but a mixture of structures such as [CH₂=C=CHCH, CHC=O]⁺, [CH₂=CHCH=CCH=C=0]⁺, etc. is assigned to the substituted phenols. Fragmentation pathways of these [C₆H₅O] isomers are also presented and discussed.