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價鍵異構體（Valence isomer），或稱作價異構體，是結構異構的一種，因分子中的價電子分佈發生了變化，並改變了分子的幾何形狀，故稱作價鍵異構。在有機化學中，特指能經週環反應進行互換的化合物。^[1]例如苯的化學式C₆H₆就不只有目前的模樣，杜瓦苯就是另一種擁有完全相同化學式，但其幾何形狀卻不同的化合物。除了杜克苯，在拓樸學的角度上，(CH)₆這一家族還有極多可能的組合。但並非所有可能的組合都實際存在；這是因為環狀化合物的鍵長及鍵角的張力限制了其可能性。

环丁二烯

环丁二烯最简单的[n]-轮烯（[4]-轮烯），它也有几种异构体。

环丁二烯的價鍵異構體
环丁二烯
正四面体烷
Bicyclo-1.1.0-but-1(3)-ene

苯

苯的價鍵異構體
苯，6個C-H鍵合連成環狀
杜瓦苯，另一個結合6個C-H鍵而環狀的方法
稜柱烷，呈稜柱體的結構
盆苯，另一個苯的異構體
聯環丙烯，兩個環丙烯連結起來的化合物，這是其中較穩定的異構體

環辛四烯

除了(CH)6有為數不少的價鍵異構體，(CH)8家族同樣有價鍵異構體。而且與其他異構體的情況一樣，當分子體積增加，可能的異構體的數目亦會相對增加。

環辛四烯及其價鍵異構體
環辛四烯 1,3,5,7-cyclooctatetraene
桶烯 Bicyclo[2.2.2]octa-2,5,7-triene
立方烷 Pentacyclo[4.2.0.0^2,5.0^3,8.0^4,7]octane
楔形烷 Pentacyclo[3.3.0.0 ^2,4.0^3,7.0^6,8]octane
半瞬烯 (4as,4bs)-2a,2b,4a,4b-Tetrahydrocyclopropa[cd]pentalene
1,5-dihydropentalene
2a,2b,4a,4b-Tetrahydrocyclopropa[cd]pentalene
Bicyclo[4.2.0]octa-2,4,7-triene.^[2]^[3]^[4]
Tricyclo[3,3,0,0^2,6]octa-3,8-diene.^[5]^[6]^[7]^[8]
Tricyclo[4,2,0,0^2,5]octa-3,7-diene.^[9]
Tetracyclo[3,3,0,0^2,4,0^3,6] octa-7-ene.^[10]
Tetracyclo[4,2,0,0^2,4,0^3,5] octa-7-ene.^[11]
Pentacyclo[5.1.0.0^2,4. 0^3,5.0^6,8]octane (octabisvalene).^[12]
Tricyclo[5.1.0.0^2,8]octa-3,5-diene (octavalene).^[13]^[14]

[10]轮烯

[10]轮烯的價鍵異構體

萘

萘的價鍵異構體
萘
薁
2a,4a,6a,6b-tetrahydrocyclopenta[cd]pentalene
Isotriquinacene 4,4a,6a,6b-tetrahydro-Cyclopenta[cd]pentalene
1,3-dicyclopentylcyclopentane
1-Cyclodecene-3,9-diyne
1,1'-Bi(cyclopentane)-1,2',3,4'-tetraene
1-phenyl-bicyclo[1.1.0]butane
3-phenylcyclobutene
(5E,7Z)-1,3,5,7,9-Cyclodecapentaene
(1β,2α,3β,6β,7α,8β)-Tetracyclo[6.2.0.0^2,7.0^3,6]deca-4,9-diene
1,3,4,5-Tetrahydrocycloprop[f]indene
1,1a,6,6a-tetrahydro-Cycloprop[a]indene
1,4-Cyclo-1,4,4a,8a-tetrahydronaphthalene
Tricyclo[6.2.0.0^3,6]deca-1,3(6),7-triene
2,5-dimethoxythiophene
Tricyclo[5.3.0.0^2,8]deca-3,5-diene
4,7-dihydro-4,7-Methano-2H-indene
3a,4,5,7a-tetrahydro-1,4,5-Metheno-1H-indene
Snoutene 2,2a,2b,3,5a,5b-hexahydro-1,2,3-metheno-1H-cycloprop[cd]indene
Lumibullvalene 1,3a,4,6a-tetrahydro-1,4-Ethenopentalene
Bicyclo[4.2.2]deca-2,4,7,9-tetrene
2a,2b-Ethano-4a,4b-dihydrocyclopropa[cd]pentalene
Hypostrophene Tetracyclo[5.3.0.0^2,6.0^3,10]deca-4,8-diene
Octahydro-3-methylene-1,2-Methanodicyclopropa(cd,gh)pentalene
Basketene Pentacyclo[4.4.0.0^2,5.0^3,8.0^4,7]dec-9-ene
Pentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decane-2-ene
Pentaprismane Hexacyclo[4.4.0.0^2,5.0^3,9.0^4,8.0^7,10]decane
Diademane Octahydro-1,2,3-metheno-1H-dicycloprop[cd,hi]indene
瞬烯 Tricyclo[3.3.2.0^2,8]deca-3,6,9-triene
2,3-dihydro-1,3-methano-1h-indene
Bicyclo[4.3.1]deca-2,4,6,8-tetraene
4,7-Methano-4,7-dihydro-1H-indene
Tricyclo[4.2.2.0^2,5]deca-3,7,9-triene
Bicyclo[4.2.2]deca-2,4,7,9-tetraene
Hexacyclo[6.2.0.0^1,9.0^2,4.0^3,5.0^7,9]decane
2a,2b,6a,6b-Tetrahydrocyclopropa[cd]azulene
(2S,3S,6S,7S)-Pentacyclo[4.4.0.0^2,5.0^3,8.0^4,7]dec-9-ene
(1R,5R,6S,7S,8R,10S)-Hexacyclo[6.2.0.0^2,4.0^2,10.0^3,6.0^5,7]decane

參考文獻

^ International Union of Pure and Applied Chemistry (IUPAC), The IUPAC Compendium of Chemical Terminology，4-th ed. (The Gold Book) (1997)。在線校正版: (1994) "Valence isomer"。doi:10.1351/goldbook.V06590
^ Huisgen, R.; Mietzsch, F. The Valence Tautomerism of Cyclooctatetraene. Angewandte Chemie International Edition in English. 1964, 3 (2): 83. doi:10.1002/anie.196400831.
^ Bicyclo[4,2,0]octa-2,4,7-triene Emanuel Vogel, H. Kiefer, W. R. Roth Volume 3, Issue 6, pages 442–443, June 1964 doi:10.1002/anie.196404422
^ Huisgen, Rolf.; Konz, Will E.; Gream, George E. Evidence for different valence tautomers of bromocyclooctatetraene. Journal of the American Chemical Society. 1970, 92 (13): 4105. doi:10.1021/ja00716a048.
^ Meinwald, Jerrold; Tsuruta, Haruki. Tricyclo[3.3.0.02,6]octa-3,7-diene. Journal of the American Chemical Society. 1969, 91 (21): 5877. doi:10.1021/ja01049a034.
^ Meinwald, Jerrold; Schmidt, Douglass. Semibullvalene from tricyclo[3.3.0.02,6]octane. Journal of the American Chemical Society. 1969, 91 (21): 5877. doi:10.1021/ja01049a033.
^ Zimmerman, Howard Elliot; Robbins, Jeffrey D.; Schantl, Joachim. C8H8 interconversions. An unusual rearrangement providing a new route to semibullvalene. Journal of the American Chemical Society. 1969, 91 (21): 5878. doi:10.1021/ja01049a035.
^ Meinwald, Jerrold.; Tsuruta, Haruki. (CH)8 hydrocarbons. Photochemistry of tricyclo[3.3.0.02,6]octa-3,7-diene. Journal of the American Chemical Society. 1970, 92 (8): 2579. doi:10.1021/ja00711a078.
^ Untersuchungen in der Cyclobutanreihe, XII. Zwei stereoisomere Dimere des Cyclobutadiens Margarete Avram, Ilie G. Dinulescu, Elise Marica, Georg Mateescu, Elvira Sliam, Costin D. Nenitzescu Chemische Berichte Volume 97, Issue 2, pages 382–389, February 1964 doi:10.1002/cber.19640970210
^ Methyl tetracyclo[3.3.0.0^2,4O^3,6]cot-7-ene-4-carboxylate Gerhard W. Klumpp, W. G. J. Rietman, J. J. Vrielink J. Am. Chem. Soc., 1970, 92 (17), pp 5266–5267 doi:10.1021/ja00720a071
^ Synthesis and reactions of tetracyclo[4.2.0.0^2,4.0^3,5]octanes Leverett R. Smith, George E. Gream, Jerrold Meinwald J. Org. Chem., 1977, 42 (6), pp 927–936 doi:10.1021/jo00426a001
^ (Z)-3,7 Bis(phenylsulfonyl)pentacyclo[5.1.0.02,4.03,5.06,8]octane, an Octabisvalene Derivative (1985) Angewandte Chemie International Edition in English Volume 24, Issue 5, pages 411–412 doi:10.1002/anie.198504111
^ The synthesis of octavalene (tricyclo[5.1.0.02,8]octa-3,5-diene) and several substituted octavalenes Tetrahedron Volume 42, Issue 6, 1986, Pages 1585-1596 Manfred Christl, Reinhard Lang and Clemens Herzog doi:10.1016/S0040-4020(01)87575-X
^ Electronic structure of octavalene. Photoelectron spectroscopic investigations Rolf Gleiter, Peter Bischof, Manfred Christl J. Org. Chem., 1986, 51 (15), pp 2895–2898 doi:10.1021/jo00365a007