Ambulation of Incipient Proton during Gas-Phase Dissociation of Protonated Alkyl Dihydrocinnamates

The Journal of Organic Chemistry
Sihang XuAthula B Attygalle

Abstract

Upon activation in the gas phase, protonated alkyl dihydrocinnamates undergo an alcohol loss. However, the mechanism followed is not a simple removal of an alkanol molecule after a protonation on the alkoxy group. The mass spectrum of the m/z 166 ion for deuteron-charged methyl dihydrocinnamate showed two peaks of 1:5 intensity ratio at m/z 133 and 134 to confirm that the incipient proton is mobile. The proton initially attached to the carbonyl group migrates to the ring and randomizes before a subsequent transfer of one of the ring protons to the alkoxy group for the concomitant alcohol elimination. Moreover, protonated methyl dihydrocinnamate undergoes more than one H/D exchange. The spectra recorded from m/z 167 and 168 ions obtained for di- and tri-deuterio isotopologues showed peak pairs at m/z 134, 135 and 135, 136, at 1:2 and 1:1 intensity ratios, respectively, confirming the benzenium ion intermediate achieves complete randomization before the proton transfer. Additionally, protonated higher esters of alkyl dihydrocinnamates undergo a cleavage of the O-CH2 bond to form an ion/neutral complex, which, upon activation, dissociates generating a carbenium ion and dihydrocinnamic acid, or rearranges to generate protonated dih...Continue Reading

References

Apr 15, 2005·Analytical Chemistry·Robert B CodyH Dupont Durst
Mar 29, 2014·Journal of the American Society for Mass Spectrometry·Jason B BialeckiAthula B Attygalle

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Citations

Nov 9, 2016·Journal of the American Society for Mass Spectrometry·Isra HassanAthula B Attygalle
May 31, 2017·Rapid Communications in Mass Spectrometry : RCM·Dejan NikolićRichard B van Breemen
Mar 27, 2019·Journal of Mass Spectrometry : JMS·Jürgen SchmidtLudger A Wessjohann

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