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Dissociative protonation and proton transfers: fragmentation of alpha, beta-unsaturated aromatic ketones in mass spectrometry.
J Org Chem. 2008 May 02; 73(9):3369-76.JO

Abstract

In mass spectrometry of the alpha,beta-unsaturated aromatic ketones, Ph-CO-CH=CH-Ph', losses of a benzene from the two ends and elimination of a styrene are the three major fragmentation reactions of the protonated molecules. When the ketones are substituted on the right phenyl ring, the electron-donating groups are in favor of losing a styrene to form the benzoyl cation, PhCO(+), whereas the electron-withdrawing groups strongly favor loss of benzene of the left side to form a cinnamoyl cation, Ph'CH=CHCO(+). When the ketones are substituted on the left phenyl ring, the substituent effects on the reactions are reversed. In both cases, the ratios of the two competitive product ions are well-correlated with the sigma p(+) substituent constants. Theoretical calculations indicate that the carbonyl oxygen is the most favorable site for protonation, and the olefinic carbon adjacent to the carbonyl is also favorable especially when a strong electron-releasing group is present on the right phenyl ring. The energy barrier to the interconversion between the ions formed from protonation at these two sites regulates the overall reactions. Transfer of a proton from the carbonyl oxygen to the ipso position on either phenyl ring, which is dissociative, triggers loss of benzene.

Authors+Show Affiliations

Department of Chemistry, Zhejiang University, Hangzhou, China.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

18370421

Citation

Hu, Nan, et al. "Dissociative Protonation and Proton Transfers: Fragmentation of Alpha, Beta-unsaturated Aromatic Ketones in Mass Spectrometry." The Journal of Organic Chemistry, vol. 73, no. 9, 2008, pp. 3369-76.
Hu N, Tu YP, Liu Y, et al. Dissociative protonation and proton transfers: fragmentation of alpha, beta-unsaturated aromatic ketones in mass spectrometry. J Org Chem. 2008;73(9):3369-76.
Hu, N., Tu, Y. P., Liu, Y., Jiang, K., & Pan, Y. (2008). Dissociative protonation and proton transfers: fragmentation of alpha, beta-unsaturated aromatic ketones in mass spectrometry. The Journal of Organic Chemistry, 73(9), 3369-76. https://doi.org/10.1021/jo702464b
Hu N, et al. Dissociative Protonation and Proton Transfers: Fragmentation of Alpha, Beta-unsaturated Aromatic Ketones in Mass Spectrometry. J Org Chem. 2008 May 2;73(9):3369-76. PubMed PMID: 18370421.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Dissociative protonation and proton transfers: fragmentation of alpha, beta-unsaturated aromatic ketones in mass spectrometry. AU - Hu,Nan, AU - Tu,Ya-Ping, AU - Liu,Yaqin, AU - Jiang,Kezhi, AU - Pan,Yuanjiang, Y1 - 2008/03/28/ PY - 2008/3/29/pubmed PY - 2008/6/17/medline PY - 2008/3/29/entrez SP - 3369 EP - 76 JF - The Journal of organic chemistry JO - J Org Chem VL - 73 IS - 9 N2 - In mass spectrometry of the alpha,beta-unsaturated aromatic ketones, Ph-CO-CH=CH-Ph', losses of a benzene from the two ends and elimination of a styrene are the three major fragmentation reactions of the protonated molecules. When the ketones are substituted on the right phenyl ring, the electron-donating groups are in favor of losing a styrene to form the benzoyl cation, PhCO(+), whereas the electron-withdrawing groups strongly favor loss of benzene of the left side to form a cinnamoyl cation, Ph'CH=CHCO(+). When the ketones are substituted on the left phenyl ring, the substituent effects on the reactions are reversed. In both cases, the ratios of the two competitive product ions are well-correlated with the sigma p(+) substituent constants. Theoretical calculations indicate that the carbonyl oxygen is the most favorable site for protonation, and the olefinic carbon adjacent to the carbonyl is also favorable especially when a strong electron-releasing group is present on the right phenyl ring. The energy barrier to the interconversion between the ions formed from protonation at these two sites regulates the overall reactions. Transfer of a proton from the carbonyl oxygen to the ipso position on either phenyl ring, which is dissociative, triggers loss of benzene. SN - 0022-3263 UR - https://www.unboundmedicine.com/medline/citation/18370421/Dissociative_protonation_and_proton_transfers:_fragmentation_of_alpha_beta_unsaturated_aromatic_ketones_in_mass_spectrometry_ L2 - https://doi.org/10.1021/jo702464b DB - PRIME DP - Unbound Medicine ER -