Substituent effect and multisite protonation in the fragmentation of alkyl benzoates

Denekamp, Chagit; Stanger, Amnon

doi:10.1002/jms.291

Cited by 12 publications

(10 citation statements)

References 24 publications

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“…A recent report dealt with the fragmentation of protonated alkyl benzoates,20 which is similar to the work presented here but not aimed at applying the kinetic method in the fragmentation of molecular species. High‐level theoretical calculations were performed to determine the favorable protonation site and to characterize the ion‐neutral complex intermediates involved 20. The reaction described therein gives rise to an alkyl cation and protonated benzoic acid.…”

Section: Resultsmentioning

confidence: 98%

Fragmentation of conjugated amides at the CC(O) bond in electrospray mass spectrometry: a proton‐bound dimeric intermediate identified by the kinetic method

Tu¹

2004

Rapid Comm Mass Spectrometry

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Fragmentation of protonated amides in mass spectrometry at the CC(O) bond, which competes with the C(O)N bond cleavage, was observed when the amide group is conjugated with an unsaturated moiety. In the case of N‐methylbenzamides bearing different substituents, this reaction gives rise to protonated methyl isocyanate and protonated benzenes. The kinetic method was applied to this reaction in spite of the fact that this is a fragmentation of a molecular species (rather than proton‐bound dimers). A correlation is established between the intensities of the two product ions and the proton affinities (PAs) of the corresponding fragment molecules, which is similar to that when the kinetic method is used in the determination of PAs on proton‐bound dimers. This result provides strong evidence that the reaction proceeds via a proton‐bound methyl isocyanate/benzene complex intermediate. In addition, the PA of isocyanic acid, which is involved in the fragmentation of unsubstituted benzamide, is compared with that of benzene and a downward revised value, 175 kcal/mol, is recommended. Copyright © 2004 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 98%

Fragmentation of conjugated amides at the CC(O) bond in electrospray mass spectrometry: a proton‐bound dimeric intermediate identified by the kinetic method

Tu¹

2004

Rapid Comm Mass Spectrometry

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“…a). Previously, the formation of protonated benzoic acid as a product ion has been observed upon chemical ionization of alkyl benzoates . However, further fragmentation of protonated benzoic acid has not been discussed.…”

Section: Resultsmentioning

confidence: 99%

Collision‐induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene

Pavlov

Attygalle

2017

J. Mass Spectrom.

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Upon activation in the gas phase, protonated benzoic acid (m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide (H - O ═ C ≡ O, m/z 45), or a molecule of carbon dioxide to yield protonated benzene (m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO or benzene loss, protonated benzoic acid transfers the charge-imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion-neutral complex between benzene and protonated CO . The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans-cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO within the ion-neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright © 2017 John Wiley & Sons, Ltd.

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“…Other benzyl cyanides substituted by a carbonyl group present less ambiguous situations. Experimental results concerning acetophenones, methyl benzoates, and benzamides as summarized in Scheme . For these six examples, it was generally assumed that protonation occurred on the oxygen of the carbonyl groups.…”

Section: Unsaturated Cyanidesmentioning

confidence: 99%

Gas phase basicities of polyfunctional molecules. Part 6: Cyanides and isocyanides

Bouchoux

2017

Mass Spectrometry Reviews

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This paper gathers structural and thermochemical informations related to the gas-phase basicity of molecules containing cyanides (nitriles) and isocyanides (isonitriles) functional groups. It constitutes the sixth part of a general review devoted to gas-phase basicities of polyfunctional compounds. A large corpus of cyanides and isocyanides molecules is examined under seven major chapters. In the first one, a rapid overview of the definitions and methods leading to gas-phase basicity, GB, proton affinity, PA, and protonation entropy, Δ S°, is given. In the same chapter, several aspects of the gas phase chemistry of protonated cyanides and isocyanides are also presented. Chapters II-VI detail the protonation energetics of aliphatic, unsaturated, and heteroatom substituted (halogens, O, S, N, P) cyanides. A seventh chapter is devoted to isocyanides. Experimental data available in the literature (120 references) were reevaluated according to the presently adopted basicity scale that is the NIST database anchored to PA(NH ) = 853.6 kJ/mol and GB (NH ) = 819 kJ/mol. In this latter source, however, several erroneous values have been identified which were corrected in the present review. Structural and energetic information given by G4MP2 quantum chemistry computations on ca. 60 typical systems are presented. The present review includes the GB, PA, and Δ S° values of ca. 110 cyanides and isocyanides, and, for selected examples, is completed by a set of computed heats of formation (Δ H°) at 0 and 298 K.

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Substituent effect and multisite protonation in the fragmentation of alkyl benzoates

Cited by 12 publications

References 24 publications

Fragmentation of conjugated amides at the CC(O) bond in electrospray mass spectrometry: a proton‐bound dimeric intermediate identified by the kinetic method

Fragmentation of conjugated amides at the CC(O) bond in electrospray mass spectrometry: a proton‐bound dimeric intermediate identified by the kinetic method

Collision‐induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene

Gas phase basicities of polyfunctional molecules. Part 6: Cyanides and isocyanides

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