Intermediacy of Proton‐Bound Dimers and Ion/Dipole Complexes in the Unimolecular Decompositions of Dialkyl‐Peroxide Radical Cations: Evidence for a coupled proton and hydrogen‐atom transfer

Schalley, Christoph A.; Schröder, Detlef; Schwarz, Helmut

doi:10.1002/hlca.19950780808

Cited by 9 publications

(4 citation statements)

References 36 publications

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“…1) were prepared by catalytic oxidation of the corresponding alkanes in the presence of the Keggin-type heteropolytungstate (TBA) 4 water). After 9 hours of reaction, cyclohexane gave 57% of cyclohexyl hydroperoxide (1), 6% of cyclohexanol and 13% of cyclohexanone.…”

Section: Methodsmentioning

confidence: 99%

“…1,2 Although alkyl hydroperoxides have been studied by various mass spectrometric techniques, [3][4][5][6][7] there appear to be no reported studies on the gas-phase chemistry of negative ions of hydroperoxides produced by chemical ionisation (CI) (CH 4 ). For a comprehensive review of the fragmentation behaviour of deprotonated organic molecules, [MÀH] À , see Ref.…”

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confidence: 99%

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Negative chemical ionisation and collision induced fragmentations of deprotonated hydroperoxides

Domingues

Simões

Cardoso

et al. 1999

Rapid Commun. Mass Spectrom.

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The mass spectra and the collisional induced dissociations (CID) of deprotonated hydroperoxides, generated by negative chemical ionisation (NCI) with methane as ionising reagent, have been examined. The chemical ionisation mass spectra of hydroperoxides show that the base peak corresponds to the [(MÀH)ÀO]À ion for all the compounds studied with the exception of t-butyl hydroperoxide. The O 2 H À ion is present in the spectra of all of these compounds that do not possess a phenyl group. This study provides detailed information on the fragmentation behaviour of deprotonated hydroperoxides, [ Received 26 October 1998; Revised 14 November 1998; Accepted 15 November 1998 An important class of organic peroxides are the hydroperoxides (RÀOÀO-H). They have a well-earned reputation for instability both to shock and heat. Nevertheless, many are stable to both distillation and sublimation.1 The structures and amounts of hydroperoxides are usually determined by physical methods (gas chromatography, adsorption and liquid-liquid partition chromatography, paper and thin layer chromatography, and polarography), and also by chemical reduction methods and colorimetric and photometric methods.1,2 Although alkyl hydroperoxides have been studied by various mass spectrometric techniques, 3-7 there appear to be no reported studies on the gas-phase chemistry of negative ions of hydroperoxides produced by chemical ionisation (CI) (CH 4 ). For a comprehensive review of the fragmentation behaviour of deprotonated organic molecules, [MÀH] À , see Ref. 8. In this work, the fragmentation mechanism of deprotonated hydroperoxides, generated by NCI with methane as ionising reagent, is investigated. EXPERIMENTALCompounds 1 and 2 (Fig. 1) were prepared by catalytic oxidation of the corresponding alkanes in the presence of the Keggin-type heteropolytungstate (TBA) 4 PW 11 Fe(H 2 O)-O 39 Á2H 2 O and hydrogen peroxide (30 wt.% solution in water). After 9 hours of reaction, cyclohexane gave 57% of cyclohexyl hydroperoxide (1), 6% of cyclohexanol and 13% of cyclohexanone. 9 In the case of cyclooctane, we obtained 68% of cyclooctyl hydroperoxide (2) and 32% of cyclooctanone after 12 hours of reaction at 80°C in acetonitrile. 10The reactions were stopped with aqueous sodium hydrogen sulfite solution, extracted with dichloromethane, and the organic layer was dried with anhydrous sodium sulphate. Compounds 3, 4 and 5 (Fig. 1) were purchased from Aldrich and used without further purification.Negative CI mass spectra and tandem mass spectra were acquired with a VG AutoSpecQ (Micromass, UK). Methane was used as the CI reagent gas at a pressure of 5 Â 10 À4 mbar. The ion source temperature was maintained at 220°C. Compounds 1, 2, 3 and 5 were introduced into the mass spectrometer using a Konik gas chromatograph (HRGC-3000C). The main reason for this is that, since the compounds are extremely volatile, the S/N ratio of the massanalysed ion kinetic energy (MIKE) spectra, when using the direct insertion probe, was low. A 30 m DB-5 capillary column was used....

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Negative chemical ionisation and collision induced fragmentations of deprotonated hydroperoxides

Domingues

Simões

Cardoso

et al. 1999

Rapid Commun. Mass Spectrom.

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“…It is formed by the ionic fragment and the zwitterionic piperazine fragment derived from the same precursor ion, which was stable enough to be detectable ( m/z 345, Scheme 3d). Such ion‐dipole complex formations in the gas phase were described in several studies [52–57] and occur when the energy threshold for the direct precursor decomposition is not reached. The complex formation enables reorientations, thereby allowing for transfers or reactions between parts of the molecule otherwise not possible due to the remoteness in the precursor molecule [54] .…”

Section: Resultsmentioning

confidence: 95%

Quantum Chemistry‐based Molecular Dynamics Simulations as a Tool for the Assignment of ESI‐MS/MS Spectra of Drug Molecules

Schnegotzki

Koopman

Grimme

et al. 2022

Chemistry A European J

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In organic mass spectrometry, fragment ions provide important information on the analyte as a central part of its structure elucidation. With increasing molecular size and possible protonation sites, the potential energy surface (PES) of the analyte can become very complex, which results in a large number of possible fragmentation patterns. Quantum chemical (QC) calculations can help here, enabling the fast calculation of the PES and thus enhancing the mass spectrometry-based structure elucidation processes. In this work, the previously unknown fragmentation pathways of the two drug molecules Nateglinide (45 atoms) and Zopiclone (51 atoms) were investigated using a combination of generic formalisms and calculations conducted with the Quantum Chemical Mass Spectrometry (QCxMS) program. The computations of the de novo fragment spectra were conducted with the semi-empirical GFNn-xTB (n = 1, 2) methods and com-pared against Orbitrap measured electrospray ionization (ESI) spectra in positive ion mode. It was found that the unbiased QC calculations are particularly suitable to predict nonevident fragment ion structures, sometimes contrasting the accepted generic formulation of fragment ion structures from electron migration rules, where the "true" ion fragment structures are approximated. For the first time, all fragment and intermediate structures of these large-sized molecules could be elucidated completely and routinely using this merger of methods, finding new undocumented mechanisms, that are not considered in common rules published so far. Given the importance of ESI for medicinal chemistry, pharmacokinetics, and metabolomics, this approach can significantly enhance the mass spectrometry-based structure elucidation processes and contribute to the understanding of previously unknown fragmentation pathways.

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“…Decomposition of peroxides mainly results in homolytic O−O bond cleavage. C−O bond cleavage of peroxides is rare under photolysis or pyrolysis but has been observed in some cases and is common in acid- or base-catalyzed decompositions …”

Section: Characterizationmentioning

confidence: 99%

Selective Preparation of Oxygen-Rich [60]Fullerene Derivatives by Stepwise Addition of tert-Butylperoxy Radical and Further Functionalization of the Fullerene Mixed Peroxides

et al. 2004

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tert-Butylperoxy radicals add to C(60) selectively to form multi-adducts C(60)(O)(m)(OO(t)Bu)(n) (m = 0, n = 2, 4, 6; m = 1, n = 0, 2, 4, 6) in moderate yields under various conditions. Visible light irradiation favors epoxide formation. High concentration of tert-butylperoxy radicals mainly produces the hexa-homoadduct C(60)(OO(t)Bu)(6) 6; low concentration and long reaction time favor the epoxy-containing C(60)(O)(OO(t)Bu)(4) 7. The reaction can be stopped at the bis-adducts with limited TBHP. A stepwise addition mechanism is discussed involving mono-, allyl-, and cyclopentadienyl C(60) radical intermediates. m-CPBA reacts with the 1,4-bis-adduct to form C(60)(O)(OO(t)Bu)(2) and C(60)(O)(3)(OO(t)Bu)(2). The C-O bond of the epoxy ring in 7 can be cleaved with HNO(3) and CF(3)COOH. Nucleophilic addition of NaOMe to 7 follows the S(N)1 and extended S(N)2' mechanism, from which four products are isolated with the general formula C(60)(O)(a)(OH)(b)(OMe)(c)(OO(t)Bu)(d). Visible light irradiation of the hexa-adduct 6 results in partial cleavage of both the C-O and O-O bonds of peroxide moieties and formation of the cage-opened compound C(60)(O)(O)(2)(OO(t)Bu)(4). All the fullerene derivatives are characterized by spectroscopic data. A single-crystal structure has been obtained for an isomer of C(60)(O)(OH)(2)(OMe)(4)(OO(t)Bu)(2).

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Intermediacy of Proton‐Bound Dimers and Ion/Dipole Complexes in the Unimolecular Decompositions of Dialkyl‐Peroxide Radical Cations: Evidence for a coupled proton and hydrogen‐atom transfer

Cited by 9 publications

References 36 publications

Negative chemical ionisation and collision induced fragmentations of deprotonated hydroperoxides

Negative chemical ionisation and collision induced fragmentations of deprotonated hydroperoxides

Quantum Chemistry‐based Molecular Dynamics Simulations as a Tool for the Assignment of ESI‐MS/MS Spectra of Drug Molecules

Selective Preparation of Oxygen-Rich [60]Fullerene Derivatives by Stepwise Addition of tert-Butylperoxy Radical and Further Functionalization of the Fullerene Mixed Peroxides

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