Cycloheptatriene

Cycloheptatriene (CHT) is an organic compound with the formula C7H8. It is a closed ring of seven carbon atoms joined by three double bonds (as the name implies) and four single bonds. This colourless liquid has been of recurring theoretical interest in organic chemistry. It is a ligand in organometallic chemistry and a building block in organic synthesis. Cycloheptatriene is not aromatic, as reflected by the nonplanarity of the methylene bridge (-CH2-) with respect to the other atoms; however the related tropylium cation is.

Cycloheptatriene
Names
Preferred IUPAC name
Cyclohepta-1,3,5-triene[1]
Other names
1,3,5-Cycloheptatriene
1H-[7]Annulene
CHT
Tropilidene
Identifiers
3D model (JSmol)
506066
ChEBI
ChemSpider
ECHA InfoCard 100.008.061
EC Number
  • 208-866-3
1943
UNII
UN number 2603
Properties
C7H8
Molar mass 92.141 g·mol−1
Density 0.888 g/mL at 25 °C
Melting point −80 °C (−112 °F; 193 K)
Boiling point 116 °C (241 °F; 389 K)
Insoluble in water
Acidity (pKa) 36
Hazards
GHS pictograms
GHS Signal word Danger
H225, H301, H304, H311, H315, H319, H335
P210, P233, P240, P241, P242, P243, P261, P264, P270, P271, P280, P301+310, P302+352, P303+361+353, P304+340, P305+351+338, P312, P321, P322, P330, P331, P332+313, P337+313, P361, P362
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

Albert Ladenburg first generated cycloheptatriene in 1881 by the decomposition of tropine.[2][3] The structure was finally proven by the synthesis of Richard Willstätter in 1901. This synthesis started from cycloheptanone and established the seven membered ring structure of the compound.[4]

Cycloheptatriene can be obtained in the laboratory by photochemical reaction of benzene with diazomethane or the pyrolysis of the adduct of cyclohexene and dichlorocarbene.[5] A related classic synthesis for cycloheptatriene derivatives, the Buchner ring enlargement, starts with the reaction of benzene with ethyl diazoacetate to give the corresponding norcaradiene ethyl ester, which then undergoes a thermally-allowed electrocyclic ring expansion to give 1,3,5-cycloheptatriene 7-carboxylic acid ethyl ester.[6][7]

The Buchner ring expansion, a classical synthesis for cycloheptatriene derivatives

Reactions

Removal of a hydride ion from the methylene bridge gives the planar and aromatic cycloheptatriene cation, also called the tropylium ion. A practical route to this cation employs PCl5 as the oxidant.[8] CHT behaves as a diene in Diels–Alder reactions. Many metal complexes of cycloheptatriene are known, including Cr(CO)3(C7H8) [9] and cycloheptatrienemolybdenum tricarbonyl.[10]

Structure of Mo(C7H8)(CO)3.

Cyclooctatetraene and cycloheptatriene are used as a triplet quencher for rhodamine 6G dye lasers.[11][12]

See also

References
  1. Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 223. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  2. A. Ladenburg (1883). "Die Constitution des Atropins". Justus Liebig's Annalen der Chemie. 217 (1): 74–149. doi:10.1002/jlac.18832170107.
  3. A. Ladenburg (1881). "Die Zerlegung des Tropines". Berichte der Deutschen Chemischen Gesellschaft. 14 (2): 2126–2131. doi:10.1002/cber.188101402127.
  4. R. Willstätter (1901). "Synthesen in der Tropingruppe. I. Synthese des Tropilidens". Justus Liebig's Annalen der Chemie. 317 (2): 204–265. doi:10.1002/jlac.19013170206.
  5. H.E. Winberg (1959). "Synthesis of Cycloheptatriene". Journal of Organic Chemistry. 24 (2): 264–265. doi:10.1021/jo01084a635.
  6. Buchner, et al., Ber., 18, 2377 (1885);
  7. For a variation: Irvin Smith Lee; Tawney Pliny O (1934). "Studies on the Polymethylbenzenes. IX. Addition of Ethyl Diazoacetate to Durene". J. Am. Chem. Soc. 56 (10): 2167–2169. doi:10.1021/ja01325a054.
  8. Conrow, K. (1973). "Tropylium Fluoroborate" (PDF). Organic Syntheses, Collected Volume. 5: 1138.
  9. James H. Rigby, Kevin R. Fales (2004). "7α-ACETOXY-(1Hβ, 6Hβ)-BICYCLO[4.4.1]UNDECA-2,4,8-TRIENE VIA CHROMIUM-MEDIATED HIGHER ORDER CYCLOADDITION". Organic Syntheses.; Collective Volume, 10, p. 1
  10. Green, Malcolm L. H.; Ng, Dennis K. P. (1995). "Cycloheptatriene and -enyl Complexes of the Early Transition Metals". Chemical Reviews. 95 (2): 439–473. doi:10.1021/cr00034a006.
  11. Tomi Nath Das; K. Indira Priyadarsini (1994). "Triplet of Cyclooctatetraene : Reactivity and Properties". Journal of the Chemical Society, Faraday Transactions. 90 (7): 963–968. doi:10.1039/ft9949000963.
  12. R. Pappalardo; H. Samelson; A. Lempicki (1970). "Long Pulse Laser Emission From Rhodamine 6G Using Cyclooctatetraene". Applied Physics Letters. 16 (7): 267–269. Bibcode:1970ApPhL..16..267P. doi:10.1063/1.1653190.
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