Collision-induced dissociation study of stereospecific elimination processes of stereoisomeric phenylcyclohexanols and their derivatives upon electron ionization

✍ Scribed by Khaselev, N.; Mandelbaum, A.

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 508 KB
• Volume: 33
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199809)33:9<819::aid-jms690>3.0.co;2-7

✦ Synopsis

The electron ionization (EI)-induced elimination of water, methanol and acetic acid from the ions of stereoiso-M'm eric 2-, 3-and 4-phenylcyclohexanols and their methyl ethers and acetates, respectively, was studied by deuteration and collision-induced dissociation (CID) techniques. The highly stereospeciÐc elimination processes in trans-3-and -4-phenylcyclohexanols and in the corresponding methyl ethers and acetates take place with the involvement of the benzylic hydrogen atom, suggesting syn-1,3-and syn-1,4-elimination via cyclic transition states. The elimination processes from the cis-alcohols and their methyl ethers occur mainly after ring opening, and result in the formation of mixtures of product ions. The elimination processes are non-stereospeciÐc in the stereoisomeric 2-phenyl-substituted systems, and are preceded by ring cleavage in both cis-and trans-isomers, resulting in mixtures of cyclic and acyclic product ions. All cis-2-, -3-and -4-phenylcyclohexyl acetates undergo elimination by a McLa †erty-type mechanism with the abstraction of a hydrogen atom from positions 2 and/or 6. An interesting outcome of this work is that the majority of the gas-phase isomeric hydrocarbon radical cations, phenyl-C 6 H 9 formed either by EI-induced fragmentation of stereoisomeric phenylcyclohexyl derivatives or by EI of a variety of isomers, retain their structural integrities. On the other hand, the CID spectra of the even-electron phenyl-C 6 H 9 ions produced by chemical ionization (CI)-induced fragmentation from isomeric phenylcyclohexa-phenyl-C 6 H 10 ' nols and their methyl ethers and acetates are similar, indicating loss of structural information under CI in this system.