Rearrangements in the fragmentation of the radical cations of azoxybenzene and of isomeric dichloroazoxybenzenes (original) (raw)

An unusual electron impact induced fragmentation of methylbenzofurazans

Organic Mass Spectrometry, 1976

The electron impact mass spectra of 4and 5-methylbenzofurazans exhibit an ion corresponding to the loss of CHO from the molecular ion. Loss of NO from the molecular ion is quite unimportant, in contrast to the behaviour of benzofurazan and some other substituted benzofurazans, in which loss of NO is the dominant process.

Electron impact-induced fragmentation of 2,1-benzisothiazoline 2,2-dioxide

Organic Mass Spectrometry, 1993

The electron impact-induced fragmentation patterns of 2,l-benzisothiazoline 2,Mioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked-scan), parent ion. and constant neutral loss spectra in metastable and collision-induced dissociation modes and deuterium labelling.

Electron impact-induced fragmentation of 2,3-dihydro-1,5-benzothiazepin-4(5H)-ones

Organic Mass Spectrometry, 1994

The electron impact-induced fragmentations of 2,3-dihydro-l,5-henzothiazepin-4(5H)-ones and some related compounds were investigated. On the basis of low-and high-resolution measurements, metastable ion studies by means of mass-analysed ion kinetic energy spectroscopy and collision-induced dissociation experiments, the main fragmentation pathways were established. The effect of methyl and phenyl substituents at the C(2) and C(3) positions of the heterocyclic ring on the fragmentations was also studied. The (1,3) ring splitting was investigated in some detail, using semi-empirical molecular orbital calculations.

Pre-ionization effects in the mass spectrometry of some azoxybenzenes

Organic Mass Spectrometry, 1988

The mass spectrometry of azoxybenzene, and of several of its substituted variants, has been investigated under both electron ionization (EI) and chemical ionization (CI) conditions. The EI spectra largely confirm earlier mechanistic conclusions of Bowie et ui. (J. C k m . SOC. B, 621 (1%7)), but extend this work to consideration of the mechanism of formation of the [M -01'' ion. This unexpected ion has been shown, using techniques of tandem mass spectrometry, to arise from pre-ionization reduction to the corresponding azobenzene probably at the ion source surfaces. These pre-ionization effects cause the observed spectra to vary markedly with the conditions, including partial pressure of the sample, within the EI source. Under CI conditions (both methane and isobutane reagent gases) the pre-ionization reduction process is even more marked, and can involve reductive cleavage to the appropriate substituted anilines. Addition of water vapour favours the latter process over formation of [M -0 + HI+.

The effect of electron-withdrawing groups in the fragmentation of the radical anions of benzyl phenyl ethers

2009

The objective of this paper is to compare the influence of two electron-withdrawing groups in the fragmentation of 2-methoxy-4-nitrophenyl benzyl ether and 4-cyanophenyl benzyl ether once these species are reduced. The stability of the corresponding radical anions depends essentially on those substituents. In our design we have chosen two species that are able to attach the electron but which have each a different capacity to retain it. An experimental study is carried out by EPR spectroscopy to analyze the different electronic nature of the generated radical anions. In addition, electronic structure calculations at the DFT level of theory have been performed to study those radical anions and their fragmentation pathways. The thermodynamics and kinetics of the two fragmentations are discussed and compared in detail.

Total Electron Detachment and Induced Cationic Fragmentation Cross Sections for Superoxide Anion (O2−) Collisions with Benzene (C6H6) Molecules

International Journal of Molecular Sciences, 2022

In this study, novel experimental total electron detachment cross sections for O2− collisions with benzene molecules are reported for the impact energy range (10–1000 eV), as measured with a transmission beam apparatus. By analysing the positively charged species produced during the collision events, relative total ionisation cross sections were derived in the incident energy range of 160–900 eV. Relative partial ionisation cross sections for fragments with m/z ≤ 78 u were also given in this energy range. We also confirmed that heavier compounds (m/z > 78 u) formed for impact energies between 550 and 800 eV. In order to further our knowledge about the collision dynamics governing the fragmentation of such heavier molecular compounds, we performed molecular dynamics calculations within the framework of the Density Functional Theory (DFT). These results demonstrated that the fragmentation of these heavier compounds strongly supports the experimental evidence of m/z = 39–42, 50, 60 ...

Electron impact mass spectra of some 1-(2-furyl)- and 1-(2-thienyl)-2-(2-benzothiazolyl)ethenes

Rapid Communications in Mass Spectrometry, 1995

The electron impact mass spectra of some 1-(2-furyl)-and 1-(2-thienyl)-2-(2-benzothiazolyl) ethenes have been recorded and the identity of various ions in the mass spectra established. The compounds examined (1-10) exhibit two main fragmentation routes. On one hand, fragmentation of the furan and thiophene nuclei and the formation of cyclopropenylethyne cations with very significant abundance and on the other hand, fragmentation of the benzothiazole nuclei on characteristic pathways. Compounds 6-10 also show two additional fragmentation routes.

A study of the electron impact fragmentation of aliphatic and alicyclic β-dioximes

OMS, Organic mass spectrometry, 1987

New Mass Spectra A Study of the Electron Impact Fragmentation of Aliphatic and Alicyclic p-Dioximes There exist a number of reports on the mass spectra of various types of mono xi me^'-^ and u-dioximes? However, p-dioximes have received no attention. The present study was conducted as part of a major investigation on p-dioximes as photochemical precursors to important heterocycles. The results are discussed in terms of two main divisions representing the two classes of the molecules examined: (i) aliphatic p-dioximes 1-6 and (ii) alicyclic p-dioximes 7-9. R1 R2 R3 R1 R2 R3 R4

Side-Chain Fragmentation of Arylalkanol Radical Cations. Carbon−Carbon and Carbon−Hydrogen Bond Cleavage and the Role of α- and β-OH Groups

Journal of the American Chemical Society, 1996

A product analysis and kinetic study of the one-electron oxidation of a number of 1-arylpropanols, 1,2diarylethanols, and some of their methyl ethers by potassium 12-tungstocobaltate(m) (abbreviated as Co(IIf;W) in aqueous acetic acid wag carried out and complemented by pulse radiolysis experiments. The oxidations occur via radical cations which undergo side-chain fragmentation involving the Co-H and/or Co-Cp bond. With 1-(4methoxyphenyl)-2-methoxypropane (1). only deprotonation ofthe radical cation is observed. In contrast, removing the ring methoxy groirp leads to exclusive C-C bond cleavage in the radical cation. Replacing the side-chain p-OMe by B-OH, the radical cation undergoes both C-C and C-H bond cleavage, with both pathways being base catalyzed. C-C bond breaking in the radical cation is also enhanced by an cr-OH group, as shown by 1-(4.methoxyphenyl)l 2,2-dimethyl-1-propanol , where this pathway, which is also base catalyzed, is the only one observed. Interestingly, a-and B-OH groups exhibit a very similar efficiency in assisting the C-C bond cleavage route in the radical cations, as is evident from the kinetic and products study of the oxidation of 1-phenyl-2-(4-methoxyphenyl)ethanol (5) 3nd 1-(4-methoxyphenyl)-2-phenylethanol (6) by Co(Itr)W, and from pulse radiolysis experiments on 5 and 6. C-C bond cleavage is the main reaction for bsth radical cations which exhibit a very similar rate of fragmentation (ft : 2.0 and 3.2 x l}a s-1, respectively). In both fragmentation reactions a small solvent isotope effect, /<(HzO)lk(D2O) (1.4 for 5'+ and 1.2 îor 6'+) and negative activation entropies are observed. These data suggest that a key role in the assistance by o.-or B-OH groups to C-C bond cleavage is played by hydrogen bonding or specific solvation of these groups. The kinetic study of the oxidations promoted by Co(Itr)W has also shown that when only one group, OH or OMe, is present in the side chain (either on Co or Cp), the fragmentation step or both the electron transfer and fragmentation steps contributé to the overall oxidation rate. However, with an OH group on both carbons of the scissile ond, as in 1-(4-methoxyphenyl)-1,2-propanediol (9), the rate of C-C bond cleavage is so fast that the electron transfer step becomes rate deternining.