Contributions of C3H6O+. ions with the oxygen on the middle carbon to gas phase ion chemistry

Authors
Citation
Dj. Mcadoo, Contributions of C3H6O+. ions with the oxygen on the middle carbon to gas phase ion chemistry, MASS SPECTR, 19(1), 2000, pp. 38-61
Citations number
142
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences
Journal title
MASS SPECTROMETRY REVIEWS
ISSN journal
0277-7037 → ACNP
Volume
19
Issue
1
Year of publication
2000
Pages
38 - 61
Database
ISI
SICI code
0277-7037(200001/02)19:1<38:COCIWT>2.0.ZU;2-2
Abstract
The numerous ways in which studies of C3H6O+. ions with the oxygen on the s econd carbon have added to our knowledge of gas phase ion chemistry are rev iewed. The enol form of this ion (I) first attracted interest during early investigations of the mechanism of the McLafferty Rearrangement and later i n characterizing the double McLafferty Rearrangement. Next, it was found th at I isomerizes to the higher energy acetone ion (2). This discovery sparke d studies of the relative stabilities of ionized and neutral enol and keton e species. It also led to the discovery that 1 --> 2 surmounts a substantia l barrier and that 2 dissociates faster than the excess energy deposited in it by the isomerization can become randomly distributed; i.e., dissociatio n following 1 --> 2 is nonergodic. This fact is manifested by a more abunda nt loss of the methyl formed by isomerization and a greater associated tran slational energy release. Propene oxide and methyl vinyl ether ions also ap pear to ionize to 2 and to dissociate nonergodically. Methane is eliminated from 2 through a methyl-acetyl ion complex Characterization of this reacti on by photoionization mass spectrometry, ab initio theory, and RRKM calcula tions helped to establish that complex-mediated alkane eliminations are gen erally confined to a region just above threshold. At higher energies, becau se attractions between ions and nonpolar neutrals are weak, simple dissocia tion is too fast for complex-mediated H-transfer to compete with it. Studie s of the collision-induced dissociations of 2 demonstrate that the first el ectronically excited A state of 2 is very long-lived and efficiently releas es its energy into translational energy when the ion collides with a neutra l at low impact energies. Finally, ion-molecule reactions of 2 and acetone- containing ion clusters in the gas phase are described. (C) 2000 John Wiley & Sons, Inc.