The Cycloheptatrienylium (Tropylium) Ion

Abstract:Starting from trimethylsilyl enol ether of 1-acetyl-1,3,5-cycloheptatriene, the title 1,1-dimethyl-, 1,1-diethyl-and 1,1-dipropyl-1H-azulenium cations 6-8 were synthesized in five steps. The order of pK R + values of these cations was found to be 7>8>6. A comparison of the values between 1,1-dialkyl-and 1,1-spiroalkylated 1H-azulenium cations with the same number of carbon atoms at the 1-position provided the results of 7>1 and 8<3. The cation 8 shows a relatively lower pK R + value to those of 3 and 7 probably due to its slightly bulkier propyl groups from which solvation stabilization of 8 under the conditions suffers. An intermolecular charge-transfer interaction between the cations and dibenzo-24-crown-8 was also studied.

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“…(1)), the pK R + value can be determined, 9 which indicates thermodynamic stability for the carbocation.…”

Section: Thermodynamic Stability and Reduction Potentials Of 11-dialmentioning

confidence: 99%

Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

et al. 2006

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“…Compte tenu de son caract~re nettement aromatique, une structure plane lui fut longtemps attribu6e, sugg6r6e par des calculs th6oriques (Doering & Knox, 1954). Des spectres infrarouge et Raman furent interpr6t6s dans cette hypoth6se.…”

Section: Conformation Du Cycle Tropilidoniqueunclassified

Structure cristalline et conformation moléculaire du (1-3,3a,8a-η)-(dimethyl-5,7 4H-cyclohepta[c]thiophene)chrome tricarbonyle

Dusausoy¹,

Protas²,

Guilard³

1973

Acta Crystallogr Sect B

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The crystal structure of (1-3,3a,8a-r/)(5,7-dimethyl-4H-cyclohepta[c]thiophene)tricarbonylchromium has been determined by X-ray diffraction. The complex crystallizes in the monoclinic system, space group P21/c. Unit-cell dimensions are a = 6.75, b = 10"93, c= 19"33/~, ,8= 100 ° Y, Z= 4. The tricarbonyl chromium group is fixed on the thiophene ring. The conformation of the latter is different from that in the free ligand and the tropilidene ring has a 'boat' conformation. R= 0"059 for 552 reflexions.

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“…Compounds of the norcaradiene type, e.g. the ester (2), were reported to undergo cleavage of the three-membered ring with formation of the cycloheptatriene derivative when heated [5][6][7]91 or when treated with bases [4,6,91.…”

Section: Introductionmentioning

confidence: 99%

The Norcaradiene Problem

Maier

1967

Angew. Chem. Int. Ed. Engl.

181

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Dedicated to Professor R. Criegee on the occasion of his 65th birthdayCompounds having the norcaradiene structure are stable if one of the double bonds of the norcaradiene also belongs to a benzene ring or if C atoms I and 6 are fixed in position by a bridge. A similar effect that favors the norcaradiene form is produced by the incorporation of nitrogen atoms in positions 3 and 4. Cycloheptatriene and most of the simply substituted tropilidenes exist exclusively in the monocyclic triene form. It has been possible in some cases to detect a valence-tautorneric equilibrium between the norcaradiene and the cycloheptatriene ring system. Non-classical stabilization of compounds having norcaradiene or cycloheptatriene structure in the sense of a pseudoaromatic "homobenzene" is only very slight, if it occurs at all.

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The Cycloheptatrienylium (Tropylium) Ion

Cited by 332 publications

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Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

Structure cristalline et conformation moléculaire du (1-3,3a,8a-η)-(dimethyl-5,7 4H-cyclohepta[c]thiophene)chrome tricarbonyle

The Norcaradiene Problem

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