Formation of 2-substituted benzofuran fragment ions from 6-alkyl- and 6-aryldibenzo(d,f)(1,3)dioxepine derivatives under electron ionization—a useful precursor ion for isomeric differentiation

✍ Scribed by Michela Begala; Graziella Tocco; Gabriele Meli; Gianni Podda; Silvana A. M. Urru

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 365 KB
• Volume: 44
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.1503

✦ Synopsis

Abstract

Tandem mass spectrometry has been applied to differentiate three sets of o‐, m‐ and p‐methyl, ‐methoxy and ‐nitro‐substituted‐6‐phenyl‐dibenzo(d,f)(1,3)dioxepines. Collision‐induced dissociation (CID) experiments have been carried out on 2‐phenylbenzo[b]furan fragment ions, which originate from the decomposition of the molecular ions after their EI‐induced isomerization to spirocyclic structures. With the exception of m‐ and p‐methylphenylbenzo[b]furan isomers, which display identical CID mass spectra, the three isomeric methoxy‐ and nitrophenylbenzo[b]furan fragment ions display very characteristic CID behavior which allows unequivocal differentiation of the 6‐phenyl‐dibenzo(d,f)(1,3)dioxepine isomers. 6‐(o‐nitrophenyl)‐dibenzo(d,f)(1,3)dioxepine isomer, does not form a 2‐(o‐nitrophenyl)benzo[b]furan ion and, therefore, it can be differentiated from the m‐ and p‐ isomers based on the mere EI mass spectra. Furthermore, it shows a characteristic ion most likely due to an ortho effect between the nitro group and the dioxepine ring. Multiple stage mass spectrometric techniques (MS^n^), labeled derivatives and reference compounds were used in order to gain additional information on the structures of product ion from the CID fragmentation. Copyright © 2008 John Wiley & Sons, Ltd.