Solvolysis and Isomerization of cis‐ and trans‐1‐Bromo‐1‐(p‐anisyl)‐propene (α‐Bromoanethole) Mesomeric Vinyl Cations, Part V

Grob, C. A.; Nussbaumer, Rahel

doi:10.1002/hlca.19710540816

Cited by 12 publications

(5 citation statements)

References 11 publications

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“…[18] Normal a-arylvinyl cations are stabilized by (a-aryl)-p-p conjugation. [19] A similar trend has been observed in the bromination of alkylsubstituted phenylacetylenes in other solvents like methanol, acetic acid, and water ± acetone mixtures; this demonstrates that the bromine in the b-position does not interfere with the stabilization of the phenyl group of the vinyl cation.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

et al. 1999

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A bromine ± alkyne p complex (l max 294 nm) of 1:1 stoichiometry has been observed for the first time in the course of the bromination of 1-phenylpropyne by means of a diode-array stopped-flow technique. ); this demonstrates that the complex is actually an essential intermediate on the reaction coordinate. The bromination of a series of nine alkynes has been studied. Bromination reactions with negative apparent activation parameters lead to mixtures of E and Z vinyl dibromides, whereas reactions with positive activation energy yield the E isomers exclusively. The reason for the difference in reactivity of these alkynes compared with structurally similar alkenes most likely lies in the stability of these 1:1 charge-transfer complexes. Usually open arylvinyl cations correspond to the energetically favored product-determining intermediates; bridged bromirenium ions are formed from deactivated alkynes and react to give E isomers. The kinetic effect of alkyl groups and of p-OCH 3 , p-CN, and p-NO 2 substituents at the aryl group on the bromination of arylalkylacetylenes is discussed. Density functional calculations provide insight into the geometries, energies, and bonding of the intermediate 1:1 and 2:1 Br 2 ± acetylene complexes involved. These theoretical investigations demonstrate that the most stable trimolecular Br 2 ± Br 2 ± acetylene adduct possesses a structure very similar to a crystallographically characterized Br 2 ± Br 2 ± alkene species, which can directly yield the ionic products, Br À 3 and vinyl cation, driven by the heterolytic action of a solvent.

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Section: Resultsmentioning

confidence: 99%

Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

et al. 1999

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“…The steiic and polar effects of a -me thy l substituent in a-brorao-p-methoxystyrene were studied (38), and the results were interpreted by formulating intimate ion pairs. Stable vinyl cations have also been postulated as intermediates in the solvolvsis of triaiyl vinyl, halides and sulfonates (12, 39).…”

Section: >-C= [>=C-(xix)mentioning

confidence: 99%

Generation of vinyl cations by solvolysis reactions. A lesser known genre of carbenium ions

Subramanian¹,

Hanack²

1975

J. Chem. Educ.

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“…Since they are not influenced by the hydrogen ion concentration of the medium a mechanism involving acid-catalyzed hydration to the intermediate (3)["' can be excluded. with ordinary carbenium ions, such as the tendency to isomerize [6] or to rearrange by way of ion pairs. Detailed mechanistic studies are in progress in several laboratories.…”

Section: By C a Grub"]mentioning

confidence: 99%

“…However, charge delocalization can only occur if C-I, C-2, and C-3 have a linear arrangement, as required by the limiting allenic form. If this alignment is prevented, as in the cyclic bromodiene(6), the negligible solvolytic reactivity characteristic of vinyl halides ret u r n~[~] .Vinyl cations have many features in common[*] Prof. Dr. C. A. Grob Institut fur Organische Chemie der Universitat CH-4056 Basel, St.-Johanns-Ring 19 (Switzerland)…”

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Formation and Detection of Vinyl Cations

Grob

1972

Angew. Chem. Int. Ed. Engl.

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Vinyl cations ( I ) , unknown and rejected a few years ago, are now the subject of an increasing number of investigations. In these cations the formal positive charge resides on the carbon atom of an olefinic double bond. With twopresumably linearly-attached ligands they belong to the group of disubstituted carbenium ions.The objections which have frequently been raised against the existence of vinyl cations are justifiable inasmuch as simple vinyl halides ( 2 ) @=halogen) resist hydrolysis and do not precipitate silver halide from aqueous silver nitrate as is observed with alkyl halides. However, an electron donating aryl substituent in the a-position, as in (2a), can promote ionization under relatively mild conditions, as was first shown in 1964 [']. Thus a-halo styrenes ( 2 a ) react in aqueous alcohol to form ketones (via the enol), enol ethers, and acetylene derivatives by the S,I--E 1 mechanism. a- Alkenyl ( 2 b ) [' I and a-cyclopropyl substituents ( 2 c ) 131 likewise increase reactivity.The reaction rates of a-aryl substituted vinyl bromides of the type ( 2 a ) depend on substituents in the benzene ring in a predictable manner. Since they are not influenced by the hydrogen ion concentration of the medium a mechanism involving acid-catalyzed hydration to the intermediate (3)["' can be excluded.

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Solvolysis and Isomerization of cis‐ and trans‐1‐Bromo‐1‐(p‐anisyl)‐propene (α‐Bromoanethole) Mesomeric Vinyl Cations, Part V

Cited by 12 publications

References 11 publications

Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

Generation of vinyl cations by solvolysis reactions. A lesser known genre of carbenium ions

Formation and Detection of Vinyl Cations

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