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 ϩ ؒ ؒ ؒ RЈOH], were generated in the unimolecular fragmentation reactions of alkoxylated oxonium ions ROCH 2 -O ϩ (RЈ)(RЉ) (where R, RЈ = CH 3 or C 2 H 5 ; RЉ = t-or iC 4 H 9 ). By means of collision-induced dissociative ionization mass spectrometry, the neutral counterpart of this reaction was identified to be a C 5 H 8 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, CH 2 ᎐ ᎐ CH-C ϩ (CH 3 ) 2 ; the subsequent proton transfer leads to the formation of the proton-bound alkanol pair and neutral 2-methylbuta-1,3-diene (C 5 H 8 ). 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.

Intramolecular Charge Transfer in the Gas Phase: Fragmentation of Protonated Sulfonamides in Mass Spectrometry

“…During its appreciable lifetime, various chemical reactions may take place either in the ionic fragment alone or between the two partners prior to the final separation. The most common reaction is the transfer of a proton or a small alkyl carbocation from the charged to the neutral species, and in these reactions the proton affinity (PA) or carbocation affinity of the relevant neutral species dictates inter alia formation of the final product ions. The ion−neutral complex also mediates isomerization, which is another major reaction that takes place en route to the products.…”

Intramolecular transacylation: fragmentation of protonated molecules via ion‐neutral complexes in mass spectrometry

“…An interesting and important intermediate is the well‐documented non‐traditional ion‐neutral complex,9 in which the incipient ionic and neutral fragments maintain interactions with each other as a solvated system in the gas phase 10. Before the final departure, the interaction between the two partners within the complex could lead to various chemical reactions including transfer from the charged to the neutral species of a small cation (e.g., the proton11 or methyl cation12), isomerization,13 electrophilic aromatic substitution,14 or elimination of a second neutral fragment to give rise to a three‐component ion‐neutral‐neutral complex 15. In this paper, we describe an interesting reaction that involves migration of a benzoyl cation from one side to the other of an aromatic heterocyclic ring through an intermediate ion‐neutral complex.…”