Valence isomer

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In organic chemistry, two molecules are valence isomers when they are constitutional isomers that can interconvert through pericyclic reactions.[1][2]

Benzene

For example, Dewar benzene transforms spontaneously into its valence isomer benzene. The compounds both can be described as (CH)6 but the arrangement of the six carbon-hydrogen blocks is different. Besides benzene and Dewar benzene, prismane, benzvalene and bicyclopropenyl are also valence-isomers of the (CH)6 family. Topologically, more arrangements in this family are possible, though they have not been attested to in chemistry. The ring strain on angles or lengths of bonding prohibit their actual formation.

Cyclooctatetraene

The valence isomers are not restricted to isomers of benzene. Valence isomers are also seen in the series (CH)8. Due to the larger number of units, the number of possible valence isomers is also greater and at least 21:

  • Valence isomers of cyclooctatetraene
  • Cyclooctatetraene (COT)
    Cyclooctatetraene (COT)
  • Barrelene
    Barrelene
  • Cubane
    Cubane
  • Cuneane
    Cuneane
  • Semibullvalene
    Semibullvalene
  • 1,5-dihydropentalene
    1,5-dihydropentalene
  • Bicyclo[2.2.2]octa-2,5,7-triene
    Bicyclo[2.2.2]octa-2,5,7-triene
  • 2a,2b,4a,4b-Tetrahydrocyclopropa[cd]pentalene
    2a,2b,4a,4b-Tetrahydrocyclopropa[cd]pentalene
  • Bicyclo[4.2.0]octa-2,4,7-triene. Tautomer with COT by thermal 6e process or photochemical 4e process [3][4][5]
    Bicyclo[4.2.0]octa-2,4,7-triene. Tautomer with COT by thermal 6e process or photochemical 4e process [3][4][5]
  • Tricyclo[3,3,0,02,6]octa-3,8-diene. Isomerises to semibullvalene at room temperature, stable at −60 °C [6][7][8][9]
    Tricyclo[3,3,0,02,6]octa-3,8-diene. Isomerises to semibullvalene at room temperature, stable at −60 °C [6][7][8][9]
  • Tricyclo[4,2,0,02,5]octa-3,7-diene. The dimer of cyclobutadiene occurs as a cis isomer and a trans isomer. Both isomers convert to COT (symmetry forbidden hence stable) with a half-life of 20 minutes at 140 °C [10]
    Tricyclo[4,2,0,02,5]octa-3,7-diene. The dimer of cyclobutadiene occurs as a cis isomer and a trans isomer. Both isomers convert to COT (symmetry forbidden hence stable) with a half-life of 20 minutes at 140 °C [10]
  • Tetracyclo[3,3,0,02,4,03,6] octa-7-ene is only known as its 4-carbomethoxy derivative.[11]
    Tetracyclo[3,3,0,02,4,03,6] octa-7-ene is only known as its 4-carbomethoxy derivative.[11]
  • Tetracyclo[4,2,0,02,4,03,5] octa-7-ene has been prepared from benzvalene and isomerises to COT [12]
    Tetracyclo[4,2,0,02,4,03,5] octa-7-ene has been prepared from benzvalene and isomerises to COT [12]
  • Pentacyclo[5.1.0.02,4. 03,5.06,8]octane (octabisvalene) is the third saturated valence isomer. The (Z)-3,7-phenylsulfonyl derivative is stable up to 200 °C.[13]
    Pentacyclo[5.1.0.02,4. 03,5.06,8]octane (octabisvalene) is the third saturated valence isomer. The (Z)-3,7-phenylsulfonyl derivative is stable up to 200 °C.[13]
  • Tricyclo[5.1.0.02,8]octa-3,5-diene (octavalene) was reported synthesised from homobenzvalene and converts to COT at 50 °C [14][15]
    Tricyclo[5.1.0.02,8]octa-3,5-diene (octavalene) was reported synthesised from homobenzvalene and converts to COT at 50 °C [14][15]

Naphthalene

Perhaps no pair of valence isomers differ more strongly in appearance than colourless naphthalene and the intensely violet azulene.

  • The valence isomers of naphthalene
  • Naphthalene
    Naphthalene
  • Azulene
    Azulene
  • 2a,4a,6a,6b-tetrahydrocyclopenta[cd]pentalene
    2a,4a,6a,6b-tetrahydrocyclopenta[cd]pentalene
  • Isotriquinacene 4,4a,6a,6b-tetrahydro-Cyclopenta[cd]pentalene
    Isotriquinacene 4,4a,6a,6b-tetrahydro-Cyclopenta[cd]pentalene
  • 1,3-dicyclopentylcyclopentane
    1,3-dicyclopentylcyclopentane
  • 1-Cyclodecene-3,9-diyne
    1-Cyclodecene-3,9-diyne
  • 1,1'-Bi(cyclopentane)-1,2',3,4'-tetraene
    1,1'-Bi(cyclopentane)-1,2',3,4'-tetraene
  • 1-phenyl-bicyclo[1.1.0]butane
    1-phenyl-bicyclo[1.1.0]butane
  • 3-phenylcyclobutene
    3-phenylcyclobutene
  • (5E,7Z)-1,3,5,7,9-Cyclodecapentaene
    (5E,7Z)-1,3,5,7,9-Cyclodecapentaene
  • (1β,2α,3β,6β,7α,8β)-Tetracyclo[6.2.0.02,7.03,6]deca-4,9-diene
    (1β,2α,3β,6β,7α,8β)-Tetracyclo[6.2.0.02,7.03,6]deca-4,9-diene
  • 1,3,4,5-Tetrahydrocycloprop[f]indene
    1,3,4,5-Tetrahydrocycloprop[f]indene
  • 1,1a,6,6a-tetrahydro-Cycloprop[a]indene
    1,1a,6,6a-tetrahydro-Cycloprop[a]indene
  • 1,4-Cyclo-1,4,4a,8a-tetrahydronaphthalene
    1,4-Cyclo-1,4,4a,8a-tetrahydronaphthalene
  • Tricyclo[6.2.0.03,6]deca-1,3(6),7-triene
    Tricyclo[6.2.0.03,6]deca-1,3(6),7-triene
  • 2,5-dimethoxythiophene
    2,5-dimethoxythiophene
  • Tricyclo[5.3.0.02,8]deca-3,5-diene
    Tricyclo[5.3.0.02,8]deca-3,5-diene
  • 4,7-dihydro-4,7-Methano-2H-indene
    4,7-dihydro-4,7-Methano-2H-indene
  • 3a,4,5,7a-tetrahydro-1,4,5-Metheno-1H-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
    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
    Lumibullvalene 1,3a,4,6a-tetrahydro-1,4-Ethenopentalene
  • Bicyclo[4.2.2]deca-2,4,7,9-tetrene
    Bicyclo[4.2.2]deca-2,4,7,9-tetrene
  • 2a,2b-Ethano-4a,4b-dihydrocyclopropa[cd]pentalene
    2a,2b-Ethano-4a,4b-dihydrocyclopropa[cd]pentalene
  • Hypostrophene Tetracyclo[5.3.0.02,6.03,10]deca-4,8-diene
    Hypostrophene Tetracyclo[5.3.0.02,6.03,10]deca-4,8-diene
  • Tetracyclo[4.2.1.12,5.09,10]deca-3,7-diene
    Tetracyclo[4.2.1.12,5.09,10]deca-3,7-diene
  • Octahydro-3-methylene-1,2-Methanodicyclopropa(cd,gh)pentalene
    Octahydro-3-methylene-1,2-Methanodicyclopropa(cd,gh)pentalene
  • Basketene Pentacyclo[4.4.0.02,5.03,8.04,7]dec-9-ene
    Basketene Pentacyclo[4.4.0.02,5.03,8.04,7]dec-9-ene
  • Pentacyclo[5.3.0.02,5.03,9.04,8]decane-2-ene
    Pentacyclo[5.3.0.02,5.03,9.04,8]decane-2-ene
  • Pentaprismane Hexacyclo[4.4.0.02,5.03,9.04,8.07,10]decane
    Pentaprismane Hexacyclo[4.4.0.02,5.03,9.04,8.07,10]decane
  • Hexacyclo[4.4.0.02,5.03,9.04,8.07,10]decane
    Hexacyclo[4.4.0.02,5.03,9.04,8.07,10]decane
  • Diademane Octahydro-1,2,3-metheno-1H-dicycloprop[cd,hi]indene
    Diademane Octahydro-1,2,3-metheno-1H-dicycloprop[cd,hi]indene
  • Bullvalene Tricyclo[3.3.2.02,8]deca-3,6,9-triene
    Bullvalene Tricyclo[3.3.2.02,8]deca-3,6,9-triene
  • 2,3-dihydro-1,3-methano-1h-indene
    2,3-dihydro-1,3-methano-1h-indene
  • Bicyclo[4.3.1]deca-2,4,6,8-tetraene
    Bicyclo[4.3.1]deca-2,4,6,8-tetraene
  • 4,7-Methano-4,7-dihydro-1H-indene
    4,7-Methano-4,7-dihydro-1H-indene
  • Tricyclo[4.2.2.02,5]deca-3,7,9-triene
    Tricyclo[4.2.2.02,5]deca-3,7,9-triene
  • Bicyclo[4.2.2]deca-2,4,7,9-tetraene
    Bicyclo[4.2.2]deca-2,4,7,9-tetraene
  • Hexacyclo[6.2.0.01,9.02,4.03,5.07,9]decane
    Hexacyclo[6.2.0.01,9.02,4.03,5.07,9]decane
  • 2a,2b,6a,6b-Tetrahydrocyclopropa[cd]azulene
    2a,2b,6a,6b-Tetrahydrocyclopropa[cd]azulene
  • (2S,3S,6S,7S)-Pentacyclo[4.4.0.02,5.03,8.04,7]dec-9-ene
    (2S,3S,6S,7S)-Pentacyclo[4.4.0.02,5.03,8.04,7]dec-9-ene
  • (1R,5R,6S,7S,8R,10S)-Hexacyclo[6.2.0.02,4.02,10.03,6.05,7]decane
    (1R,5R,6S,7S,8R,10S)-Hexacyclo[6.2.0.02,4.02,10.03,6.05,7]decane

References

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (1994) "Valence isomer". doi:10.1351/goldbook.V06590
  2. ^ Rearrangements and interconversions of compounds of the formula (CH)n Lawrence T. Scott, Maitland. Jones Chem. Rev., 1972, 72 (2), pp 181–202 doi:10.1021/cr60276a004
  3. ^ Huisgen, R.; Mietzsch, F. (1964). "The Valence Tautomerism of Cyclooctatetraene". Angewandte Chemie International Edition in English. 3 (2): 83. doi:10.1002/anie.196400831.
  4. ^ 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
  5. ^ Huisgen, Rolf.; Konz, Will E.; Gream, George E. (1970). "Evidence for different valence tautomers of bromocyclooctatetraene". Journal of the American Chemical Society. 92 (13): 4105. doi:10.1021/ja00716a048.
  6. ^ Meinwald, Jerrold; Tsuruta, Haruki (1969). "Tricyclo[3.3.0.02,6]octa-3,7-diene". Journal of the American Chemical Society. 91 (21): 5877. doi:10.1021/ja01049a034.
  7. ^ Meinwald, Jerrold; Schmidt, Douglass (1969). "Semibullvalene from tricyclo[3.3.0.02,6]octane". Journal of the American Chemical Society. 91 (21): 5877. doi:10.1021/ja01049a033.
  8. ^ Zimmerman, Howard Elliot; Robbins, Jeffrey D.; Schantl, Joachim (1969). "C8H8 interconversions. An unusual rearrangement providing a new route to semibullvalene". Journal of the American Chemical Society. 91 (21): 5878. doi:10.1021/ja01049a035.
  9. ^ Meinwald, Jerrold.; Tsuruta, Haruki. (1970). "(CH)8 hydrocarbons. Photochemistry of tricyclo[3.3.0.02,6]octa-3,7-diene". Journal of the American Chemical Society. 92 (8): 2579. doi:10.1021/ja00711a078.
  10. ^ 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
  11. ^ Methyl tetracyclo[3.3.0.02,4O3,6]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
  12. ^ Synthesis and reactions of tetracyclo[4.2.0.02,4.03,5]octanes Leverett R. Smith, George E. Gream, Jerrold Meinwald J. Org. Chem., 1977, 42 (6), pp 927–936 doi:10.1021/jo00426a001
  13. ^ (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
  14. ^ 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
  15. ^ 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
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