Substituent effect and multisite protonation in the fragmentation of alkyl benzoates

Journal of Mass Spectrometry : JMS
Chagit Denekamp, Amnon Stanger

Abstract

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.

References

Jul 29, 1999·Journal of Mass Spectrometry : JMS·J C TraegerD J McAdoo
May 1, 1992·Journal of the American Society for Mass Spectrometry·G ThielkingH F Grützmacher

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Citations

Mar 15, 2006·Journal of the American Society for Mass Spectrometry·Chagit Denekamp, Moran Yaniv
Jun 9, 2009·Rapid Communications in Mass Spectrometry : RCM·Ya-Ping TuJack Cunniff
Jul 12, 2002·Journal of Mass Spectrometry : JMS
Aug 29, 2007·The Journal of Physical Chemistry. a·Gregory J FrancisMurray J McEwan

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