Stable carbocations. 215. Carbon-13 nuclear magnetic resonance spectroscopic study of the benzenium, naphthalenium, and anthracenium ions

Oláh, George A.; Staral, John S.; Asencio, Gregorio; Liang, Gao; Forsyth, David; Mateescu, Gheorghe D.

doi:10.1021/ja00488a001

Cited by 127 publications

(88 citation statements)

References 9 publications

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“…Instead, it is a classic carbenium ion [40] with an allylic system [32,33] and minimal, if any, homoallylic delocalization nature [32]. In other studies, the benzenium ion is shown to be stabilized via hyperconjugation [40,[45][46][47], where the overlap between the bonds of CH 2 and the bonds of remaining carbons in the ring creates cyclic delocalization.…”

Section: Resultsmentioning

confidence: 99%

“…Studies of [C 6 H 7 ] ϩ (known as "benzenium ion", "protonated benzene", "cyclohexadienyl cation") in solution and in the gas phase using NMR [31,32], IR . Cleavages leading to major fragment ions in ␣-linolenic acid methyl ester.…”

Section: Resultsmentioning

confidence: 99%

“…Their calculations predicted two electronic transitions in the visible region, which was in good agreement with their experimental results. The benzenium ion is also stabilized by a 1,2-hydrogen shift (scrambling) [32][33][34][35] where at room temperature the hydrogens migrate on the six carbons at a high speed, thus delocalizing the positive charge. Interestingly, protonated polyaromatic hydrocarbons, including benzenium ions, have been found to be stable species in interstellar space [48].…”

Section: Resultsmentioning

confidence: 99%

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Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

Hejazi

Ebrahimi

Guilhaus

et al. 2009

J. Am. Soc. Mass Spectrom.

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There is a consensus that electron impact ionization mass spectrometry is not capable of discriminating among geometrical isomers of unsaturated fatty acid methyl esters (and in general olefinic compounds). In this paper, we report the identification of all eight geometrical isomers of ␣-linolenic acid, one of the few essential -3 fatty acids that has attracted great attention, using low-energy electron ionization mass spectrometry. Three electron energies 70, 50, and 30 eV were studied and the mass spectrum of each isomer was obtained from the analysis of different concentrations of a standard mixture of ␣-linolenic acid methyl ester geometrical isomers to ensure the robustness of the method. Principal component analysis was employed to model the complex variation of m/z intensities across the isomers. Only using the data of 30 eV energy was complete differentiation among geometrical isomers observed. The unique cleavage pattern of the ␣-linolenic acid methyl ester isomers leading to a benzenium ion structure is discussed and general fragmentation rules are derived using the mass spectra of over 300 compounds with different kinds and levels of unsaturation. Application of the proposed method is not limited to ␣-linolenic acid. It can potentially be used to identify the geometrical isomers of any compounds with an olefinic chain. (J Am Soc Mass Spectrom 2009, 20, 1272-1280

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

Hejazi

Ebrahimi

Guilhaus

et al. 2009

J. Am. Soc. Mass Spectrom.

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“…The benzenium ion corresponds to a side-on adduct of the phenyl cation and H 2 having C 2v symmetry [46], and H 2 loss proceeds with monotonically increasing potential energy towards the dissociation limit. Isolable arenium ions are known, and the benzenium ion itself, C 6 H 7 + , has been inferred from NMR spectroscopy of superacidic solutions [47] and on the basis of X-ray crystallography [48].…”

Section: Thermochemistrymentioning

confidence: 99%

Intermediates in the Methanol-to-hydrocarbons (MTH) Reaction: A Gas Phase Study of the Unimolecular Reactivity of Multiply Methylated Benzenium Cations

et al. 2006

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In order to reach a deeper insight into the reaction mechanism of the zeolite catalyzed methanol to hydrocarbons reaction (MTH), the proposed reaction intermediates, i.e., a series of multiply methyl-substituted benzenium ions has been generated in the gas phase by chemical ionization. The fragmentations of the corresponding long-lived (metastable) ions have been investigated. While expulsion of H 2 dominates for the lower homologues, elimination of methane dominates for the higher homologues, accompanied by increasing amounts CH 3 . Loss of larger fragments relevant to the MTH-reaction, in particular ethene, propene and even butene, is also observed in minor amounts. This latter finding is consistent with a proposed reaction cycle in the MTH reaction known as the paring mechanism, and the feasibility of this mechanism has thus been demonstrated. The metastable gasphase ions studied here are considerably more energetic than those residing in a zeolite catalyst, but they were found to decompose with markedly higher selectivity towards alkenes as compared to those activated by collision-induced dissociation (CID).

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“…This same observation is evident from the 9,lO-dimethylanthracenium dication [43] (34), in which the anthracene protons are observed in the chemical shift range of 6 8.83-8.26 (S02C1F, SbF,). The I3C NMR chemical shifts for cationic species provide a better probe for charge distribution in T-cations [44] and dications [45]. Structural alternative 32 is ruled out based on considerations of the l3C NMR chemical shifts without ambiguity.…”

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confidence: 99%

An observable model for the S_N2 transition state [1a]. Hypervalent trigonal bipyramidal carbon (10‐C‐5) [1b]

Forbus

Martin

1993

Heteroatom Chemistry

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Stable carbocations. 215. Carbon-13 nuclear magnetic resonance spectroscopic study of the benzenium, naphthalenium, and anthracenium ions

Cited by 127 publications

References 9 publications

Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

Intermediates in the Methanol-to-hydrocarbons (MTH) Reaction: A Gas Phase Study of the Unimolecular Reactivity of Multiply Methylated Benzenium Cations

An observable model for the S_N2 transition state [1a]. Hypervalent trigonal bipyramidal carbon (10‐C‐5) [1b]

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Stable carbocations. 215. Carbon-13 nuclear magnetic resonance spectroscopic study of the benzenium, naphthalenium, and anthracenium ions

Cited by 127 publications

References 9 publications

Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

Intermediates in the Methanol-to-hydrocarbons (MTH) Reaction: A Gas Phase Study of the Unimolecular Reactivity of Multiply Methylated Benzenium Cations

An observable model for the SN2 transition state [1a]. Hypervalent trigonal bipyramidal carbon (10‐C‐5) [1b]

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An observable model for the S_N2 transition state [1a]. Hypervalent trigonal bipyramidal carbon (10‐C‐5) [1b]