Experimenteller und theoretischer Nachweis der entarteten Isomerisierung via Kohlenstoff-Platzwechsel beim Cyclopentylkation in der Gasphase

Franke, Wilfried; Schwarz, Helmut; Thies, Helga; Chandrasekhar, Jayaraman; Schleyer, Paul von Ragué; Hehre, Warren J.; Saunders, Martin; Walker, Gary E.

doi:10.1002/ange.19800920630

Cited by 10 publications

(2 citation statements)

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“…Further, there have been several experimental investigations aimed at studying the isomerization of alkylcyclopentyl cations. [48][49][50][51] However, there has not been a complete investigation of ring formation via carbocation routes specifically aimed at understanding the catalytic steps toward aromatization in acid zeolite systems.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental investigations of carbocation chemistry, dating back to Olah's successful attempt of stabilizing carbocations in superacid solutions, exist and provide important insight into potential cyclization mechanisms. − For example, Saunders et al give experimental evidence for protonated cyclopropane intermediates for several carbocation reactions, reporting activation energies for various reactions using line shape analysis of 1 H NMR data. Further, there have been several experimental investigations aimed at studying the isomerization of alkylcyclopentyl cations. − However, there has not been a complete investigation of ring formation via carbocation routes specifically aimed at understanding the catalytic steps toward aromatization in acid zeolite systems.…”

Section: Introductionmentioning

confidence: 99%

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DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

2003

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We conducted density functional theory calculations to identify the complete cyclization mechanism (ring formation and ring expansion) for protonated hexadiene in the gas-phase as a precursory means of studying aromatization of light alkanes in acidic zeolite catalysts. We identify the rate-determining step to consist of ring expansion from a methylcyclopenta carbenium precursor to a stable cyclohexa carbenium intermediate, exhibiting an activation barrier of 9.6 kcal/mol and proceeding through a bicyclic intermediate starting from a secondary cyclopentyl carbocation. This pathway for ring closure was preferred over tertiary precursor expansion and direct cyclization to a cyclohexyl carbocation. Expecting carbocation intermediates to be represented by alkoxide species near Brønsted acid sites, we calculated the relative stability of primary, secondary, and tertiary alkoxide analogues to cyclopentyl carbocation intermediates involved in ring expansion and notice a reversal of stability relative to gas-phase carbocation stabilities (i.e., primary > secondary > tertiary stability). However, on the basis of the notion that transition state stability depends heavily on carbocation character of the transition state, even in alkoxide-based chemistry, we conclude that ring expansion would nevertheless constitute the rate-determining step in a zeolite-catalyzed mechanism.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

2003

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Pyramidale Carbokationen

Schwarz

1981

Angew. Chem.

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Carbokationen mit pyramidenförmiger Struktur können als die Bindeglieder zwischen der Organischen und der Anorganischen Chemie angesehen werden. Aus Vorstellungen vom elektronischen Aufbau dieser Spezies werden Konsequenzen für Struktur, Ladungsverteilung und Reaktivität (Abfangreaktionen mit Nucleophilen) abgeleitet. Phänomene der Gasphasenchemie von Kationen, z. B. das Kohlenstoff‐„Scrambling”︁ bei Carbenium‐Ionen, lassen sich durch pyramidal strukturierte Zwischenstufen oder Übergangszustände erklären. Die Möglichkeit von Übergangszuständen mit H2 als 1„side‐on”︁‐ oder „end‐on”︁‐Liganden und ihre Bedeutung für den Mechanismus unimolekularer Prozesse werden diskutiert.

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Pyramidal Carbocations

Schwarz

1981

Angew. Chem. Int. Ed. Engl.

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Dedicated to Professor Ferdinand Bohlmann on the occasion of his 60th birthday Pyramidal cations are discussed with reference to their role as the connecting link between organic and inorganic chemistry. The electronic structure of these ions is treated with respect to their physical and chemical properties, namely charge distribution, geometry, and quenching reactions with nucleophiles. The chemistry in the gas phase of certain carbenium ions, in particular the scrambling of carbon atoms, is readily explicable by invoking transition states or intermediates of pyramidal structure. Moreover, the behavior of unimolecular processes can be understood in terms of transition states in which a hydrogen molecule is positioned as a "side-on" or an "end-on" ligand. Volume 20 -Number 12 December 1981 Pages 991 -1 066 Angew. Chem. Inr. Ed. Engl. 20. 991-1003 (1981) 0 Verlag Chemie GmbH. 6940 Weinheim, 1981 0570-0833/81/1212-0991 $02.50/0 ( 73) Nu ( 74) NU I \ I I D Scheme 7. Quenching of pyramidal cations by nucleophiles Nue. Angew. Chem. Int. Ed. Engl. 20. 991-1003 (198I) Received: July 8, 1981 [Z 390 IE] German version: Angew. Chem. 93, 1046 (1981) 11) a) H. Hogeueen. P. W. Kwant. Acc. Chem. Res. 8, 413 (1975); b) H. C. Brown (with comments by P. uon R. Schleyer): The Nonclassical Ion Problem, Plenum Press, New York 1977, Chap. 1, p. 17.121 a) R. N. Grimes: Carboranes, Academic Press, New York 1970; b) W. N .

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Experimenteller und theoretischer Nachweis der entarteten Isomerisierung via Kohlenstoff-Platzwechsel beim Cyclopentylkation in der Gasphase

Cited by 10 publications

References 12 publications

DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

Pyramidale Carbokationen

Pyramidal Carbocations

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