Claisen rearrangement of allyl phenyl ether and its sulfur and selenium analogues on electron impact

Prabhakar, S.; Mirza, Shama P.; Kundu, Anupam; Roy, Sujit; Vairamani, M.

doi:10.1002/1097-0231(20000715)14:13<1116::aid-rcm997>3.0.co;2-w

Cited by 7 publications

(3 citation statements)

References 16 publications

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“…Rearrangement reactions play a major role in the solution phase, which can sometimes be a direct pathway for critical transformations. Many solution‐phase rearrangements are also studied in the ion source of a mass spectrometer, a procedure suitable for exploring the fundamental nature of the rearrangements in the absence of solvent 1–5. The electron impact (EI) source is useful for the study of intramolecular rearrangements, because the fragmentation processes under EI conditions are unimolecular processes.…”

Section: Methodsmentioning

confidence: 99%

Mass spectral study of O‐ and S‐aryl dimethylthiocarbamates under electron impact conditions: Newman‐Kwart rearrangement in the gas phase

Prabhakar

Kar

Mirza

et al. 2001

Rapid Comm Mass Spectrometry

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The electron impact (EI) mass spectra of isomeric S-and O-aryl (2-naphthyl, R-Ph-= aryl, where R = H, NO 2 , COOCH 3 , COCH 3 and OCH 3 ) dimethylthiocarbamates have been studied in detail. The EI spectra of O-aryl dimethylthiocarbamates include some of the fragment ions that are characteristic of the corresponding S-aryl isomer, which could be explained by a Newman-Kwart rearrangement in the ion source of the mass spectrometer, after ionization. The EI mass spectra of S-aryl dimethylthiocarbamates showed specific fragment ions resulting from cleavage of the molecular ion involving the bond between sulfur and the carbonyl group of the carbamate moiety (a-cleavage). The EI mass spectra of O-aryl dimethylthiocarbamates, however, showed the fragmentation of the molecular ion by a-cleavage involving the bonds on both sides of oxygen atom. Further, the EI mass spectra of O-aryl dimethylthiocarbamates containing an electron-withdrawing substituent (-R) on the aryl group showed a characteristic fragment ion corresponding to [M À R] . Copyright # 2001John Wiley & Sons, Ltd.Mass spectrometry continues to be a sensitive tool not only for the characterization of compounds of different nature, but also for the study of gas-phase reactions. Rearrangement reactions play a major role in the solution phase, which can sometimes be a direct pathway for critical transformations. Many solution-phase rearrangements are also studied in the ion source of a mass spectrometer, a procedure suitable for exploring the fundamental nature of the rearrangements in the absence of solvent. 1±5 The electron impact (EI) source is useful for the study of intramolecular rearrangements, because the fragmentation processes under EI conditions are unimolecular processes. One such intramolecular rearrangement is the Newman-Kwart rearrangement of O-aryl dialkylthiocarbamates found under solution-phase conditions. 6±14 A number of phenols have been converted to the corresponding thiol compounds by exploiting the NewmanKwart rearrangement (Scheme 1). Mass spectral analyses of reaction products of the Newman-Kwart rearrangement have not been reported in the literature, to our knowledge. Hence, a detailed study of the behaviour of isomeric S-aryl and O-aryl dimethylthiocarbamates under EI conditions was undertaken, and the results are presented. EXPERIMENTALThe S-aryl dimethylthiocarbamates (1, 3, 5, 7 and 9; Scheme 2) were prepared from the corresponding O-aryl dimethylthiocarbamates (2, 4, 6, 8 and 10; Scheme 2) under microwave irradiation. 15 The structures of all the compounds were characterized by IR, NMR and mass spectrometry. Mass spectra were recorded using a Micromass Autospec M mass spectrometer equipped with an OPUS V3.IX data system, using a dedicated EI source. The source conditions were: accelerating voltage 7 kV, electron energy 70 eV, trap current 200 mA, and source temperature 250°C. Spectra were acquired using the data system with a scan time of 1s/decade and 0.5 s interscan delay. All the samples were introduced through an HP 5890 seri...

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Section: Methodsmentioning

confidence: 99%

Mass spectral study of O‐ and S‐aryl dimethylthiocarbamates under electron impact conditions: Newman‐Kwart rearrangement in the gas phase

Prabhakar

Kar

Mirza

et al. 2001

Rapid Comm Mass Spectrometry

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“…One rearrangement of this kind in the gas phase is the Claisen rearrangement which has been observed in a large number of different phenylpropargyl ethers and allyl phenyl ethers, and has been well documented 12–15. Most of these compounds which undergo the Claisen rearrangement under electron impact conditions produce abundant [M − CO] + ions.…”

Section: Methodsmentioning

confidence: 99%

Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalines

Starke

Sarodnick

Ovcharenko

et al. 2001

Rapid Comm Mass Spectrometry

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The electron impact (EI) mass spectra of 34 differently substituted 2-phenoxymethyl-, 2-naphthyloxymethyl-, 2-pyridinyloxymethyl- and 2-chinolinyloxymethylquinoxalines were recorded. The fragmentation patterns were examined by metastable ion analysis and exact mass measurements, employing finally also selective deuterium labelling. The inclusion of the substituted aryl ring moiety appears to be important for the fragmentation of the aryloxymethylquinoxalines. A molecular ion rearrangement is proposed for the observed loss of OH* and CHO* radicals. The influence of the different substituents on the aryl ring moiety on the rearrangement in the gas phase and on the resulting fragmentation was investigated.

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“…98,99 Prabhakar and colleagues demonstrated the occurrence of EI-induced Claisen rearrangements and Newman-Kwart rearrangements with the aid of high-resolution mass spectrometry (HRMS) and MS/MS. 100,101 They used MS/MS and ligand attachment to determine the structures of the metal complexes observed under ESI and MALDI. 102,103 They showed that information about the oxidation state and coordination number of the metal ion can be obtained in these experiments.…”

Section: Introductionmentioning

confidence: 99%

Mass Spectrometry in India

Vairamani

Prabhakar

2012

Eur J Mass Spectrom (Chichester)

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All rights reserved EUROPEAN JOURNAL OF MASS SPECTROMETRY This review highlights the research in mass spectrometry carried out all over India, with a focus on the last two decades. There has been a phenomenal increase in the use of mass spectrometers in India during the last decade following the introduction, at the beginning of the 21st century, of rugged electrospray ionization sources for the commercially available instruments, with applications such as pharmacokinetics and bio-equivalence drug studies, pesticide residue analysis and proteomics. There have been more papers published in these areas than could be fully covered in this article. This review covers mostly research in mass spectrometry carried out continuously in institutions where advanced facilities for mass spectrometry are functional. Researchers in India, with some notable exceptions, have always used and still use commercial mass spectrometers in their various areas of research, rather than develop their unique instruments. The review is divided into three parts: organic, elemental (or atomic) and biological mass spectrometry. Organic mass spectrometry Organic and bio-organic chemistry Research in organic mass spectrometry in the early years was mainly focused on the study of mass spectral fragmentation of different classes of new compounds,and was initiated in the 1960s by the late Das and his colleagues from the National Chemical Laboratory (NCL), Pune. The first double-focusing mass spectrometer (CEC-110 B) was installed at NCL for high-resolution mass measurements. The compounds studied by Das and his colleagues included aromatic amides, Benzophenanthridine derivatives, norses

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Claisen rearrangement of allyl phenyl ether and its sulfur and selenium analogues on electron impact

Cited by 7 publications

References 16 publications

Mass spectral study of O‐ and S‐aryl dimethylthiocarbamates under electron impact conditions: Newman‐Kwart rearrangement in the gas phase

Mass spectral study of O‐ and S‐aryl dimethylthiocarbamates under electron impact conditions: Newman‐Kwart rearrangement in the gas phase

Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalines

Mass Spectrometry in India

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