Carbocationic rearrangement of pivaloyl cation and protonated pivalaldehyde in superacid medium: A novel solution equivalent of the McLafferty rearrangement

Oláh, George A.; Mathew, Thomas; Goeppert, Alain; Rasul, Golam; Prakash, G. K. Surya; Esteves, Pierre M.

doi:10.1016/j.jasms.2004.05.002

Cited by 15 publications

(5 citation statements)

References 40 publications

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“…At 50 eV, the ions of m/z 575, 391 and 207 were the main product ions from sodiated nonactin. Accurate‐mass measurements revealed that these fragments derived from losses of one, two and three C 10 H 16 O 3 (184 mass units) molecules from the precursor ion ([M + Na] + ), respectively, via consecutive McLafferty‐type rearrangements (Scheme ) . These reactions had been previously described for other polyether ionophores, such as lasalocid and tetronasin .…”

Section: Resultsmentioning

confidence: 99%

Dereplication ofStreptomycessp. AMC 23 polyether ionophore antibiotics by accurate-mass electrospray tandem mass spectrometry

et al. 2014

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Actinomycetes, especially those belonging to the genus Streptomyces, are economically important from a biotechnological standpoint: they produce antibiotics, anticancer compounds and a variety of bioactive substances that are potentially applicable in the agrochemical and pharmaceutical industries. This paper combined accurate-mass electrospray tandem mass spectrometry in the full scan and product ion scan modes with compounds library data to identify the major compounds in the crude extract produced by Streptomyces sp. AMC 23; it also investigated how sodiated nonactin ([M + Na](+)) fragmented. Most product ions resulted from elimination of 184 mass units due to consecutive McLafferty-type rearrangements. The data allowed identification of four macrotetrolides homologous to nonactin (monactin, isodinactin, isotrinactin/trinactin and tetranactin) as well as three related linear dimer compounds (nonactyl nonactoate, nonactyl homononactoate and homononactyl homononactoate). The major product ions of the sodiated molecules of these compounds also originated from elimination of 184 and 198 mass units. UPLC-MS/MS in the neutral loss scan mode helped to identify these compounds on the basis of the elimination of 184 and 198 mass units. This method aided monitoring of the relative production of these compounds for 32 days and revealed that the biosynthetic process began with increased production of linear dimers as compared with macrotetrolides. These data could facilitate dereplication and identification of these compounds in other microbial crude extracts.

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Section: Resultsmentioning

confidence: 99%

Dereplication ofStreptomycessp. AMC 23 polyether ionophore antibiotics by accurate-mass electrospray tandem mass spectrometry

et al. 2014

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“…Loss of the t-butyl radical followed by McLafferty rearrangement does not seem plausible for the first loss would create an even electron ion. Although the McLafferty rearrangement has been observed for even electron systems [21,22,24,25,[30][31][32]36,41,46,49,60] , it seems unlikely to be of great importance for these systems, but it cannot be excluded for we did not investigate this possibility in more detail. The loss of just the t-butyl radical was also observed as the peaks at the highest m/z values, as well as abundant formation of [HOSi(CH 3 ) 2 ] + (m/z = 75).…”

Section: Resultsmentioning

confidence: 99%

“… The study of the major MS fragmentations of these carbonyl derivatives, however, has not received due attention. For example, although the McLafferty rearrangement of carbonyl compounds has been the focus of extensive and continuous research , studies on oximes and silyl oxime ethers have been limited. Surprisingly, to date, only one article has reported the McLafferty rearrangement for ketoximes.…”

Section: Introductionmentioning

confidence: 99%

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

et al. 2012

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The McLafferty rearrangement is an extensively studied fragmentation reaction for the odd-electron positive ions from a diverse range of functional groups and molecules. Here, we present experimental and theoretical results of 12 model compounds that were synthesized and investigated by GC-TOF MS and density functional theory calculations. These compounds consisted of three main groups: carbonyls, oximes and silyl oxime ethers. In all electron ionization mass spectra, the fragment ions that could be attributed to the occurrence of a McLafferty rearrangement were observed. For t-butyldimethylsilyl oxime ethers with oxygen in a β-position, the McLafferty rearrangement was accompanied by loss of the t-butyl radical. The various mass spectra showed that the McLafferty rearrangement is relatively enhanced compared with other primary fragmentation reactions by the following factors: oxime versus carbonyl, oxygen versus methylene at the β-position and ketone versus aldehyde. Calculations predict that the stepwise mechanism is favored over the concerted mechanism for all but one compound. For carbonyl compounds, C–C bond breaking was the rate-determining step. However, for both the oximes and t-butyldimethylsilyl oxime ethers with oxygen at the β-position, the hydrogen transfer step was rate limiting, whereas with a CH2 group at the β-position, the C–C bond breaking was again rate determining. n-Propoxy-acetaldehyde, bearing an oxygen atom at the β-position, is the only case that was predicted to proceed through a concerted mechanism. The synthesized oximes exist as both the (E)- and (Z)-isomers, and these were separable by GC. In the mass spectra of the two isomers, fragment ions that were generated by the McLafferty rearrangement were observed. Finally, fragment ions corresponding to the McLafferty reverse charge rearrangement were observed for all compounds at varying relative ion intensities compared with the conventional McLafferty rearrangement.

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“…Catalysts of these types are also suitable for complete isomerization of pivalaldehyde to methyl isopropyl ketone (62). The mechanism of the carbocationic rearrangement under superacidic activation in solution is believed to be similar to the McLafferty rearrangement reported in the gaseous phase.…”

Section: Alkylation Catalystsmentioning

confidence: 91%

Poly(vinylpyridine)

2011

Handbook of Engineering and Specialty Thermoplastics

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Carbocationic rearrangement of pivaloyl cation and protonated pivalaldehyde in superacid medium: A novel solution equivalent of the McLafferty rearrangement

Cited by 15 publications

References 40 publications

Dereplication ofStreptomycessp. AMC 23 polyether ionophore antibiotics by accurate-mass electrospray tandem mass spectrometry

Dereplication ofStreptomycessp. AMC 23 polyether ionophore antibiotics by accurate-mass electrospray tandem mass spectrometry

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

Poly(vinylpyridine)

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