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. The ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

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 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.Clayden, J.; ...

. It is a ligand in

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

and a building block in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. 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 satur ...

, as reflected by the nonplanarity of the

methylene bridge In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule with formula ; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of ...

(-CH₂-) with respect to the other atoms; however the related

tropylium cation In organic chemistry, the tropylium ion or cycloheptatrienyl cation is an aromatic species with a formula of 7H7sup>+. Its name derives from the molecule tropine from which cycloheptatriene (tropylidene) was first synthesized in 1881. Salts of ...

is.

Synthesis

Albert Ladenburg Albert Ladenburg (July 2, 1842August 15, 1911) was a German chemist. Early life and education Ladenburg was a member of the well-known Jewish in Mannheim. He was educated at a Realgymnasium at Mannheim and then, after the age of 15, at the tec ...

first generated cycloheptatriene in 1881 by the decomposition of

tropine Tropine is a derivative of tropane containing a hydroxyl group at the third carbon. It is also called 3-tropanol. Tropine is a central building block of many chemicals active in the nervous system, including tropane alkaloids. Some of these comp ...

. The structure was finally proven by the synthesis of

Richard Willstätter Richard Martin Willstätter FRS(For) HFRSE (, 13 August 1872 – 3 August 1942) was a German organic chemist whose study of the structure of plant pigments, chlorophyll included, won him the 1915 Nobel Prize for Chemistry. Willstätter invented ...

in 1901. This synthesis started from

cycloheptanone Cycloheptanone, (CH2)6CO, is a cyclic ketone also referred to as suberone. It is a colourless volatile liquid. Cycloheptanone is used as a precursor for the synthesis of pharmaceuticals. Synthesis In 1836, French chemist Jean-Baptiste Boussinga ...

and established the seven membered ring structure of the compound. Cycloheptatriene can be obtained in the laboratory by

photochemical reaction Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ...

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 atoms, ...

with

diazomethane Diazomethane is the chemical compound CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow gas; thus, it is almost u ...

or the pyrolysis of the adduct of

cyclohexene Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes. Cyclohexene is not very stable upon long term storage with exposure to light a ...

and

dichlorocarbene Dichlorocarbene is the reactive intermediate with chemical formula CCl2. Although this chemical species has not been isolated, it is a common intermediate in organic chemistry, being generated from chloroform. This bent diamagnetic molecule rapidly ...

. A related classic synthesis for cycloheptatriene derivatives, the Buchner ring enlargement, starts with the reaction of

with

ethyl diazoacetate Ethyl diazoacetate (N=N=CHC(O)OC2H5) is a diazo compound and a reagent in organic chemistry. It was discovered by Theodor Curtius in 1883. The compound can be prepared by reaction of the ethyl ester of glycine with sodium nitrite and sodium aceta ...

to give the corresponding norcaradiene ethyl ester, which then undergoes a thermally-allowed electrocyclic

ring expansion Ring expansion and ring contraction reactions in the course of organic synthesis refer to a set of reactions which can lead to the expansion or contraction of an existing ring. This often makes it possible to access structures that would be dif ...

to give 1,3,5-cycloheptatriene 7-carboxylic acid ethyl ester. TOC_ACS1996v2

File:Chemical_structure_of_heptalene.png,

Heptalene Heptalene is a polycyclic hydrocarbon with chemical formula , composed of two fused cycloheptatriene rings. It is an unstable, non-planar compound which is non-aromatic. The dianion, however, satisfies Hückel's rule In organic chemistry, Hüc ...

– composed of two fused cycloheptatriene rings. File:Azulene struttura.svg,

Azulene Azulene is an organic compound and an isomer of naphthalene. Naphthalene is colourless, whereas azulene is dark blue. Two terpenoids, vetivazulene (4,8-dimethyl-2-isopropylazulene) and guaiazulene (1,4-dimethyl-7-isopropylazulene), that feature ...

– composed of fused

cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6.LeRoy H. Scharpen and Victor W. Laurie (1965): "Structure of cyclopentadiene". ''The Journal of Chemical Physics'', volume 43, issue 8, pages 2765-2766. It is often ab ...

and cycloheptatriene rings. File:Pentaheptafulvalene.png,

Sesquifulvalene Sesquifulvalene or Pentaheptafulvalene is a hydrocarbon in the fulvalene class with chemical formula C12H10. It is composed of linked cyclopentadiene and cycloheptatriene rings. Properties In the ground state, which is a singlet state, the cent ...

– composed of linked cyclopentadiene and cycloheptatriene rings. File:Elassovalene.svg, Elassovalene – composed of one cycloheptatriene and two fused cyclopentene rings. File:Tropone.png,

Tropone Tropone or 2,4,6-cycloheptatrien-1-one is an organic compound with some importance in organic chemistry as a non-benzenoid aromatic. The compound consists of a ring of seven carbon atoms with three conjugated alkene groups and a ketone group. Th ...

– composed of cycloheptatriene ring and

carbonyl group 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 containing a ...

. File:Tropolone.png,

Tropolone Tropolone is an organic compound with the chemical formula . It is a pale yellow solid that is soluble in organic solvents. The compound has been of interest to research chemists because of its unusual electronic structure and its role as a ligan ...

– 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 containing a ...

and hydroxy groups. File:Gamma-thujaplicin.png,

Hinokitiol Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive used ...

– composed of cycloheptatriene ring,

isopropyl In organic chemistry, propyl is a three-carbon alkyl substituent with chemical formula for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent is ofte ...

and hydroxy groups (

cycloheptatrienolone).

Reactions

Removal of a

hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of ...

ion from the

gives the planar and aromatic cycloheptatriene cation, also called the

tropylium In organic chemistry, the tropylium ion or cycloheptatrienyl cation is an aromatic species with a formula of 7H7sup>+. Its name derives from the molecule tropine from which cycloheptatriene (tropylidene) was first synthesized in 1881. Salts of ...

ion. A practical route to this cation employs PCl₅ as the oxidant. CHT behaves as a diene in

Diels–Alder reaction In organic chemistry, the Diels–Alder reaction is a chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene derivative. It is the prototypical example of a peric ...

s, for example with

maleic anhydride Maleic anhydride is an organic compound with the formula C2H2(CO)2O. It is the acid anhydride of maleic acid. It is a colorless or white solid with an acrid odor. It is produced industrially on a large scale for applications in coatings and poly ...

: :

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. Many ...

es of cycloheptatriene are known, including Cr(CO)₃(C₇H₈) and cycloheptatrienemolybdenum tricarbonyl. CHTMo(CO)3

Cyclooctatetraene 1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as nnulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of ...

and cycloheptatriene are used as a triplet quencher for

rhodamine 6G Rhodamine 6G is a highly fluorescent rhodamine family dye. It is often used as a tracer dye within water to determine the rate and direction of flow and transport. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with ...

dye laser A dye laser is a laser that uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths, often spanning 50 to 100 na ...

References

{{Annulenes Annulenes Seven-membered rings

Synthesis

Reactions

See also

References