Valence isomer

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:

  1. ^ Huisgen, R.; Mietzsch, F. (1964). "The Valence Tautomerism of Cyclooctatetraene". Angewandte Chemie International Edition in English 3 (2): 83. doi:10.1002/anie.196400831.
  2. ^ 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
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ 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
  9. ^ 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
  10. ^ 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
  11. ^ (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
  12. ^ 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
  13. ^ 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

Naphthalene

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

References

  1. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (1994) "Valence isomer".
  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