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Dissociative protonation sites: reactive centers in protonated molecules leading to fragmentation in mass spectrometry.
J Org Chem. 2006 Jul 21; 71(15):5482-8.JO

Abstract

It is often found in mass spectrometry that when a molecule is protonated at the thermodynamically most favorable site, no fragmentation occurs, but a major reaction is observed when the proton migrates to a different position. For benzophenones, acetophenones, and dibenzyl ether, which are all preferentially protonated at the oxygen, deacylation or dealkylation was observed in the collision-induced dissociation of the protonated molecules. For para-monosubstituted benzophenones, electron-withdrawing substituents favor the formation of RC6H4CO+ (R = substituent), whereas electron-releasing groups favor the competing reaction leading to C6H5CO+. The ln[(RC6H4CO+)/(C6H5CO+)] values are well-correlated with the sigmap+ substituent constants. In the fragmentation of protonated acetophenones, deacetylation proceeds to give an intermediate proton-bound dimeric complex of ketene and benzene. The distribution of the product ions was found to depend on the proton affinities of ketene and substituted benzenes, and the kinetic method was applied in identifying the reaction intermediate. Protonated dibenzyl ether loses formaldehyde upon dealkylation, via an ion-neutral complex of the benzyloxymethyl cation and neutral benzene. These gas-phase retro-Friedel-Crafts reactions occurred as a result of the attack of the proton at the carbon atom to which the carbonyl or the methylene group is attached on the aromatic ring, which is described as the dissociative protonation site.

Authors+Show Affiliations

Drug Metabolism and Pharmacokinetics, Roche Pharmaceuticals, 3431 Hillview Avenue, Palo Alto, California 94304, USA. yaping.tu@roche.com

Pub Type(s)

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

Language

eng

PubMed ID

16839126

Citation

Tu, Ya-Ping. "Dissociative Protonation Sites: Reactive Centers in Protonated Molecules Leading to Fragmentation in Mass Spectrometry." The Journal of Organic Chemistry, vol. 71, no. 15, 2006, pp. 5482-8.
Tu YP. Dissociative protonation sites: reactive centers in protonated molecules leading to fragmentation in mass spectrometry. J Org Chem. 2006;71(15):5482-8.
Tu, Y. P. (2006). Dissociative protonation sites: reactive centers in protonated molecules leading to fragmentation in mass spectrometry. The Journal of Organic Chemistry, 71(15), 5482-8.
Tu YP. Dissociative Protonation Sites: Reactive Centers in Protonated Molecules Leading to Fragmentation in Mass Spectrometry. J Org Chem. 2006 Jul 21;71(15):5482-8. PubMed PMID: 16839126.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Dissociative protonation sites: reactive centers in protonated molecules leading to fragmentation in mass spectrometry. A1 - Tu,Ya-Ping, PY - 2006/7/15/pubmed PY - 2007/6/15/medline PY - 2006/7/15/entrez SP - 5482 EP - 8 JF - The Journal of organic chemistry JO - J Org Chem VL - 71 IS - 15 N2 - It is often found in mass spectrometry that when a molecule is protonated at the thermodynamically most favorable site, no fragmentation occurs, but a major reaction is observed when the proton migrates to a different position. For benzophenones, acetophenones, and dibenzyl ether, which are all preferentially protonated at the oxygen, deacylation or dealkylation was observed in the collision-induced dissociation of the protonated molecules. For para-monosubstituted benzophenones, electron-withdrawing substituents favor the formation of RC6H4CO+ (R = substituent), whereas electron-releasing groups favor the competing reaction leading to C6H5CO+. The ln[(RC6H4CO+)/(C6H5CO+)] values are well-correlated with the sigmap+ substituent constants. In the fragmentation of protonated acetophenones, deacetylation proceeds to give an intermediate proton-bound dimeric complex of ketene and benzene. The distribution of the product ions was found to depend on the proton affinities of ketene and substituted benzenes, and the kinetic method was applied in identifying the reaction intermediate. Protonated dibenzyl ether loses formaldehyde upon dealkylation, via an ion-neutral complex of the benzyloxymethyl cation and neutral benzene. These gas-phase retro-Friedel-Crafts reactions occurred as a result of the attack of the proton at the carbon atom to which the carbonyl or the methylene group is attached on the aromatic ring, which is described as the dissociative protonation site. SN - 0022-3263 UR - https://www.unboundmedicine.com/medline/citation/16839126/Dissociative_protonation_sites:_reactive_centers_in_protonated_molecules_leading_to_fragmentation_in_mass_spectrometry_ L2 - https://doi.org/10.1021/jo060439v DB - PRIME DP - Unbound Medicine ER -