Role of hydrogen migration in the mechanism of acetic acid elimination from MH(+) ions of acetates on chemical ionization and collision-induced dissociation

I Kuzmenkov I; A Etinger; A MandelbaumM

doi:10.1002/(SICI)1096-9888(199908)34:8<797::AID-JMS834>3.0.CO;2-X

Role of hydrogen migration in the mechanism of acetic acid elimination from MH(+) ions of acetates on chemical ionization and collision-induced dissociation

J Mass Spectrom. 1999 Aug;34(8):797-803. doi: 10.1002/(SICI)1096-9888(199908)34:8<797::AID-JMS834>3.0.CO;2-X.

Authors

I Kuzmenkov I¹, A Etinger, A MandelbaumM

Affiliation

¹ Department of Chemistry, Technion-Israel Institute of Technology, Haifa, Israel.

PMID: 10423560
DOI: 10.1002/(SICI)1096-9888(199908)34:8<797::AID-JMS834>3.0.CO;2-X

Abstract

The elimination of acetic acid from the MH(+) ions of acetates of stereoisomeric 2-methyl-1-cyclohexanols and 1-hydroxy-trans-decalins exhibits a significant degree of stereospecificity under isobutane chemical ionization and collision-induced dissociation (CID) conditions, resulting in more abundant [MH - AcOH](+) ions in the cis-isomers 4c and 5tc than in their trans-counterparts 4t and 5tt. These findings suggest the involvement of a 1,2-hydride shift from the beta- to the alpha-position in the course of the acetic acid elimination from the MH(+) ions of the above cis-acetates, resulting in tertiary carbocation structures. The proposed mechanism of the elimination is supported by a considerable deuterium isotope effect detected in beta-deuterium-labeled cis-2-methyl-1-acetoxycyclohexane and by a CID study of the structures of the [MH - AcOH](+) ions obtained from cis- and trans-1,2-diacetoxycyclohexanes. Copyright 1999 John Wiley & Sons, Ltd.