Ion–neutral–neutral complexes in unimolecular reactions: formation of proton-bound alkanol pairs from alkoxylated oxonium ions

Abstract

The proton-bound alkanol pairs, [ROH ⋯ H⁺ ⋯ R′OH], were generated in the unimolecular fragmentation reactions of alkoxylated oxonium ions ROCH₂–O⁺(R′)(R″) (where R, R′ = CH₃ or C₂H₅; R″ = t- or iC₄H₉). By means of collision-induced dissociative ionization mass spectrometry, the neutral counterpart of this reaction was identified to be a C₅H₈ hydrocarbon molecule. It is proposed that the reactions proceed through an intermediate ion–neutral complex in which two neutral alkanol molecules are associated with the 1,1-dimethylallyl cation, CH₂CH–C⁺(CH₃)₂; the subsequent proton transfer leads to the formation of the proton-bound alkanol pair and neutral 2-methylbuta-1,3-diene (C₅H₈). This is the first three-component intermediate “ion–neutral–neutral” complex (where the ion is not a proton) identified in the unimolecular fragmentation of covalently-bonded organic ions in the gas phase.