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Substituted 3‐phenylpropenoates and related analogs: electron ionization mass spectral fragmentation and density functional theory calculations
Author(s) -
Wheelock C. E.,
Colvin M. E.,
Sanborn J. R.,
Hammock B. D.
Publication year - 2008
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.1384
Subject(s) - chemistry , halogen , intramolecular force , fragmentation (computing) , density functional theory , alkene , electrophile , chlorine , radical ion , photochemistry , ionization energy , ionization , radical substitution , computational chemistry , electron ionization , bromine , ion , stereochemistry , radical , organic chemistry , alkyl , computer science , catalysis , operating system
Analysis of ethyl 3‐(2‐chlorophenyl)propenoate by electron ionization mass spectrometry showed the distinct loss of an ortho chlorine. To characterize the structural requisites for the observed mass fragmentation, a series of 30 halogen‐substituted 3‐phenylpropenoate‐related structures were examined. All ester‐containing alkene derivatives exhibited loss of the distinctive chlorine from the 2‐position of the phenyl ring. Analogous derivatives with the halogen (chlorine or bromine) in the para position did not evidence selective halogen loss. Results demonstrated that substituted 3‐phenylpropenoates and their analogs fragment via the formation of a previously reported benzopyrylium intermediate. To understand the correlation between the intramolecular radical substitution and the abundance and selectivity of the chlorine (or other halogen) displacement, density functional theory calculations were performed to determine the charge on the principal cation involved in the chlorine loss (in the ortho, meta , and para positions), the charge for the neutral radical (noncation), the excess alpha‐electron density on the relevant atom and the energy to form the cation from the neutral atom (ionization energy). Results showed that the selectivity and extent of halogen displacement correlated highly to the electrophilicity of the radical cation as well as the neutral radical. These data further support the proposed fragmentation mechanism involving intramolecular radical elimination. Copyright © 2008 John Wiley & Sons, Ltd.