Fragmentations of Deprotonated Alkyl Hydroperoxides (ROO− Upon Collisional Activation: A Combined Experimental and Computational Study

Abstract

The collision-induced dissociation (CID) mass spectra of the [M − H]^– anions of methyl, ethyl, and tert-butyl hydroperoxides have been measured over a range of collision energies in a flowing afterglow–selected ion flow tube (FA-SIFT) mass spectrometer. Activation of the CH₃OO^– anion is found to give predominantly HO^– fragment anions whilst CH₃CH₂OO⁻ and (CH₃)₃COO^– produce HOO^– as the major ionic fragment. These results, and other minor fragmentation pathways, can be rationalized in terms of unimolecular rearrangement of the activated anions with subsequent decomposition. The rearrangement reactions occur via initial abstraction of a proton from the α-carbon in the case of CH₃OO^– or the β-carbon for CH₃CH₂OO^– and (CH₃)₃COO^–. Electronic structure calculations suggest that for the CH₃CH₂OO^– anion, which can theoretically undergo both α- and β-proton abstraction, the latter pathway, resulting in HOO^– + CH₂CH₂, is energetically preferred.