Cycloheptatriene (CHT) is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

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 Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

. It is a ligand in organometallic chemistry and a building block in organic synthesis. Cycloheptatriene is not

aromatic In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

, as reflected by the nonplanarity of the methylene bridge (-CH₂-) with respect to the other atoms; however the related tropylium cation is.

Synthesis

Albert Ladenburg first generated cycloheptatriene in 1881 by the decomposition of tropine. 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. Cycloheptatriene can be obtained in the laboratory by photochemical reaction of

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen ato ...

with diazomethane or the pyrolysis of the adduct of cyclohexene and dichlorocarbene. A related classic synthesis for cycloheptatriene derivatives, the

Buchner ring enlargement The Buchner ring expansion is a two-step organic C-C bond forming reaction used to access 7-membered rings. The first step involves formation of a carbene from ethyl diazoacetate, which cyclopropanates an aromatic ring. The ring expansion occurs ...

, starts with the reaction of

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. TOC_ACS1996v2

File:Chemical_structure_of_heptalene.png, Heptalene – composed of two fused cycloheptatriene rings. File:Azulene struttura.svg, Azulene – composed of fused cyclopentadiene and cycloheptatriene rings. File:Pentaheptafulvalene.png, Sesquifulvalene – composed of linked cyclopentadiene and cycloheptatriene rings. File:Elassovalene.svg,

Elassovalene Elassovalene (2a,8b-dihydro-cyclopent 'cd''zulene) is a polycyclic hydrocarbon with chemical formula C12H10, composed of one cycloheptatriene ring and two fused cyclopentene rings. See also * List of chemical compounds with unusual names * Azu ...

– composed of one cycloheptatriene and two fused cyclopentene rings. File:Tropone.png, Tropone – composed of cycloheptatriene ring and carbonyl group. File:Tropolone.png, Tropolone – composed of cycloheptatriene ring,

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containin ...

and hydroxy groups. File:Gamma-thujaplicin.png, Hinokitiol – composed of cycloheptatriene ring, isopropyl,

and hydroxy groups ( isopropyl cycloheptatrienolone).

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. CHT behaves as a diene in Diels–Alder reactions, for example with maleic anhydride: : Cycloheptatriene Diels-Alder reaction

Many

metal complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. Man ...

es of cycloheptatriene are known, including Cr(CO)₃(C₇H₈) and

cycloheptatrienemolybdenum tricarbonyl Cycloheptatrienemolybdenum tricarbonyl is the organomolybdenum compound with the formula (C7H8)Mo(CO)3. It is a red-orange solid that is soluble in nonpolar organic solvents. The compound has no practical value but is a prototypical complex of c ...

Cyclooctatetraene and cycloheptatriene are used as a

triplet A triplet is a set of three items, which may be in a specific order, or unordered. It may refer to: Science * A series of three nucleotide bases forming an element of the Genetic code * J-coupling as part of Nuclear magnetic resonance spectrosc ...

quencher for rhodamine 6G dye lasers.

References

{{Annulenes Annulenes Seven-membered rings