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Substituent effect and multisite protonation in the fragmentation of alkyl benzoates
Author(s) -
Denekamp Chagit,
Stanger Am
Publication year - 2002
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.291
Subject(s) - chemistry , protonation , substituent , medicinal chemistry , alkyl , fragmentation (computing) , dissociation (chemistry) , benzoates , proton affinity , stereochemistry , photochemistry , ion , organic chemistry , computer science , operating system
The dissociation of protonated alkyl benzoates (para H, CN, OMe and NO 2 ) into protonated benzoic acids and alkyl cations was studied in the gas phase. It was found that the product ratio depends on the substituent at the para position of the phenyl ring. The substituent effect is probably the result of the formation of an ion–neutral complex intermediate that decomposes to an ion and a neutral, according to the relative proton affinities of the two moieties. The experimental results and theoretical calculations indicate that the favored protonation site in these compounds is the ester's carbonyl and that proton transfer from the phenyl ring to the ester group is very likely to occur under chemical ionization conditions. It is most probable that the carbonyl protonated form is a common intermediate in the fragmentation process, regardless of the protonation site. Copyright © 2002 John Wiley & Sons, Ltd.