trans-Cyclooctene

trans-Cyclooctene is a cyclic hydrocarbon with the formula [–(CH2)6CH=CH–], where the two C–C single bonds adjacent to the double bond are on opposite sides of the latter's plane. It is a colorless liquid with a disagreeable odor.

trans-Cyclooctene[1]
Names
IUPAC name
(E)-Cyclooctene
Other names
trans-Cyclooctene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
EC Number
  • 213-245-5
Properties
C8H14
Molar mass 110.200 g·mol−1
Appearance colorless liquid
Density 0.848 g/mL
Melting point −59 °C (−74 °F; 214 K)
Boiling point 143 °C (1 atm); 68-72 °C (100 torr)[2]
Hazards
GHS pictograms
GHS Signal word Danger
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Cyclooctene is notable as the smallest cycloalkene that is readily isolated as its trans-isomer. The cis-isomer is much more stable;[3] the ring-strain energies being 16.7 and 7.4 kcal/mol,respectively.[4]

   
cis-Cyclooctene          trans-Cyclooctene   

A planar arrangement of the ring carbons would be too strained, and therefore the stable conformations of the trans form have a bent (non-planar) ring. Computations indicate that the most stable "crown" conformation has the carbon atoms alternately above and below the plane of the ring.[5] A "half-chair" conformation, with about 6 kcal/mol higher energy, has carbons 2,3,5,6, and 8 on the same side of the plane of carbons 1,4, and 7.[5]

All conformations of trans-cyclooctene are chiral (specifically, what some call planar-chiral[6]) and the enantiomers can be separated.[7][8][9] In theory, conversion of between the enantiomers can be done, without breaking any bonds, by twisting the whole –CH=CH– group, rigidly, by 180 degrees. However, that entails passing one of its hydrogens through the crowded ring.[7]

Preparation

trans-Cyclooctene was first synthesized on a preparatory scale by Arthur C. Cope with a Hofmann elimination reaction of N,N,N-trimethylcyclooctylammonium iodide.[10] The reaction gives a mixture of cis and trans isomers, and the trans isomer is selectively trapped as a complex with silver nitrate.

Other methods exist where the trans isomer is synthesized from the cis isomer in several synthetic steps. For instance, it can be prepared in almost 100% yield by converting the cis isomer to 1,2-epoxycyclootane ("cyclooctene oxide") followed by reactions with lithium diphenyphosphide LiPPh
2 and with methyl iodide CH
3I. (Similar procedures can give cis,trans isomers of 1,4-cyclooctadiene and 1,5-cyclooctadiene).[2]

In addition, a photochemical method exists for the direct cis–trans isomerisation. Although this equilibrium strongly favours the more stable cis form, the reaction can be driven towards the trans form by trapping with silver ions.[11][12]

Reactions

Because of the higher internal strain on the double bond, the trans isomer is more reactive than the cis isomer and of typical unsaturated hydrocarbons. For instance, its double bond will rapidly add tetrazine and its derivatives.[5] The compound also readily polymerizes with a ruthenium-based initiator.[4]

References
  1. "cis-Cyclooctene". Sigma-Aldrich.
  2. Edwin Vedejs, Karel A. J. Snoble, and Philip L. Fuchs (1973): "Phosphorus betaines derived from cycloheptene and cyclooctene oxides. Inversion of cyclooctenes". Journal of Organic Chemistry, volume 38, issue 6, pages 1178–1183. doi:10.1021/jo00946a024
  3. Neuenschwander, Ulrich; Hermans, Ive (2011). "The conformations of cyclooctene: Consequences for epoxidation chemistry". J. Org. Chem. 76 (24): 10236–10240. doi:10.1021/jo202176j.
  4. Ron Walker, Rosemary M. Conrad, and Robert H. Grubbs (2009): "The living ROMP of trans-cyclooctene". Macromolecules, volume 42, issue 3, pages 599–605. doi:10.1021/ma801693q
  5. Ramajeyam Selvaraj, Joseph M Fox "trans-Cyclooctene — a stable, voracious dienophile for bioorthogonal labeling". Current Opinion in Chemical Biology, volume 17, issue 5, pages 753-760 doi:10.1016/j.cbpa.2013.07.031
  6. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Planar chirality". doi:10.1351/goldbook.P04681
  7. Arthur C. Cope, C. R. Ganellin, H. W. Johnson, T. V. Van Auken, and Hans J. S. Winkler (193): "Molecular asymmetry of olefins. I. Resolution of trans-cyclooctene". Journal of the American Chemical Association, volume 85, issue 20, pages 3276–3279. doi:10.1021/ja00903a049
  8. Arthur C. Cope and Anil S. Mehta (1964): "Molecular asymmetry of olefins. II. The absolute configuration of trans-cyclooctene". Journal of the American Chemical Association, volume 86, issue 24, pages 5626–5630. doi:10.1021/ja01078a044
  9. Steven D. Paget (2001). "(−)-Dichloro(ethylene)(α-methylbenzylamine)platinum(II)". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rd119.CS1 maint: uses authors parameter (link)
  10. Cope, Arthur C.; Bach, Robert D. (1969). "trans-Cyclooctene". Organic Syntheses. 49: 39.; Collective Volume, 5, p. 315
  11. John S. Swenton (1969): "Photoisomerization of cis-cyclooctene to trans-cyclooctene". Journal of Organic Chemistry, volume 34, issue 10, pages 3217–3218. doi:10.1021/jo01262a102
  12. Royzen, Maksim; Yap, Glenn P. A.; Fox, Joseph M. (2008). "A photochemical synthesis of functionalized trans-cyclooctenes driven by metal complexation". J. Am. Chem. Soc. 130 (12): 3760–3761. doi:10.1021/ja8001919.
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