Complexes ion/molecule intermediaires dans la fragmentation des ethers protones

Audier, H. E.; Monteiro, C.; Berthomieu, Dorothée; Tortajada, Jeanine

doi:10.1016/0168-1176(91)80006-9

Cited by 24 publications

(6 citation statements)

References 14 publications

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“…The distance between the proton and the non‐protonated oxygen could be reduced if the C—O bond of the protonated primary alkoxyl is elongated. The concept of a stretched C—O bond upon protonation has been previously suggested by Audier et al ,23 who studied the fragmentation of protonated methyl isopropyl ether. Ab initio calculations showed a local minimum when the C—O bond length was 2.73 Å.…”

Section: Resultsmentioning

confidence: 98%

Proton transfer via strained transition states in the elimination of alcohols from MH⁺ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Denekamp

Mandelbaum

2001

J. Mass Spectrom.

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Section: Resultsmentioning

confidence: 98%

Proton transfer via strained transition states in the elimination of alcohols from MH⁺ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Denekamp

Mandelbaum

2001

J. Mass Spectrom.

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“…However, if an H-migration from the amine to the amide occurred simultaneously with the homolytic cleavage of the S™N bond, an amine radical cation at m/z 188 would be formed. This H-migration seems less likely since the difference in PAs between the amine and the amide is estimated to be greater than 0.5 eV (or 50 kJmol Ϫ1 ) [19], a proposed value beyond which H-exchanges no longer occur in the unimolecular decomposition of protonated species [20,21]. When the piperidine amide is proton- ated, a heterolytic C™N bond cleavage of this group gives rise to the ion at m/z 263 by elimination of a neutral amine.…”

Section: Cid Of Protonatedmentioning

confidence: 99%

Tandem mass spectrum of a growth hormone secretagogue: Amide bond cleavage and resultant gas-phase rearrangement

Qin

2002

J. Am. Soc. Mass Spectrom.

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Compound 1 {N-[1(R) Ϫ [(1,2-dihydro-1-methylsulfonylspiro[3H-indole-3,4'-piperidin]-1'-yl)carbonyl]-2-(phenylmethyloxy)ethyl]-2-amino-2-methylpropanamide}(MW 528) is an orally-active growth hormone secretagogue (GHS). As part of a continual effort to analyze the ESI/MS and MS n data of novel drugs, the ESI/MS and MS/MS data of protonated 1 (m/z 529) are analyzed and reported here. The analyses reveal that under low-energy collision-induced dissociation (CID) in an ion trap or a quadrupole collision cell, protonated 1 undergoes a gas-phase rearrangement to form protonated 3 (m/z 357) which competes with the y-and b-type product ions during the amide bond cleavages of protonated 1. It is proposed that when the b-type ion is formed by cleavage of the piperidine amide bond, piperidine (a neutral species) and the b-ion (a cation) form an ion-neutral complex. In this complex, piperidine functions as a nucleophile to attack the benzylic carbon of the b-ion, and the protonated ether group in the b-ion acts as a leaving group, which results in the migration of the benzylic group to the piperidine amine to form protonated 3. Protonated 2 (an analog of 1) was studied under the same experimental conditions. The results show that protonated 2 undergoes a similar rearrangement to form protonated 3. While this rearrangement is a relatively minor fragmentation process for protonated 1, it is a predominant process for protonated 2. This phenomenon is explained in terms of the proposed ion-neutral-complex mechanism. (J Am Soc Mass Spectrom 2002, 13, 371-377)

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“…It is probable that the reaction 1 → 3 is a concerted process. A similar mechanism has been shown to take place 15,16 3) could be loose and could correspond to a rather flat portion of the potential energy surface in which a tert-butyl cation and the allylic • OCHCH 2 radical remain in interaction. From the experimental data and from the calculation of the stable structures, the schematic energy diagram shown in Figure 4 is proposed.…”

Section: Intermediacy Of Complexesmentioning

confidence: 66%

Evidence for an Alkene Metathesis Reaction during the Unimolecular Dissociation of (CH₃)₃COCHCH₂^•+

Rest

Denhez

Chamot‐Rooke

et al. 2000

Eur J Mass Spectrom (Chichester)

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The unimolecular reaction of the metastable tert-butyl vinyl ether radical cation leads mainly to elimination of ethylene. From metastable ion studies as well as Fourier transform ion cyclotron resonance measurements and by using isotopic labeling, it is proposed that the fragmentation begins with the cleavage of the O–C(butyl) bond. This behavior, which contrasts with that of ionized alkylethers, is the consequence of the presence of a vinyl group that allows the formation of a neutral allylic radical. The key intermediate of the fragmentation is likely to be a [CH2CHOH, (CH3)2CCH2]•+ complex in which a cycloaddition–cycloreversion reaction occurs. This intermediate is the same as that produced by a McLafferty rearrangement in appropriate aldehyde radical cations.

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Complexes ion/molecule intermediaires dans la fragmentation des ethers protones

Cited by 24 publications

References 14 publications

Proton transfer via strained transition states in the elimination of alcohols from MH⁺ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Proton transfer via strained transition states in the elimination of alcohols from MH⁺ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Tandem mass spectrum of a growth hormone secretagogue: Amide bond cleavage and resultant gas-phase rearrangement

Evidence for an Alkene Metathesis Reaction during the Unimolecular Dissociation of (CH₃)₃COCHCH₂^•+

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Complexes ion/molecule intermediaires dans la fragmentation des ethers protones

Cited by 24 publications

References 14 publications

Proton transfer via strained transition states in the elimination of alcohols from MH+ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Proton transfer via strained transition states in the elimination of alcohols from MH+ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Tandem mass spectrum of a growth hormone secretagogue: Amide bond cleavage and resultant gas-phase rearrangement

Evidence for an Alkene Metathesis Reaction during the Unimolecular Dissociation of (CH3)3COCHCH2•+

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Proton transfer via strained transition states in the elimination of alcohols from MH⁺ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Proton transfer via strained transition states in the elimination of alcohols from MH⁺ ions of stereoisomeric diethers and hydroxy esters upon chemical ionization and collision‐induced dissociation

Evidence for an Alkene Metathesis Reaction during the Unimolecular Dissociation of (CH₃)₃COCHCH₂^•+