Cycloheptatriene (CHT) is an organic compound with the chemical 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 () with respect to the other atoms; however the related tropylium cation is, rendering the compound relatively suspectible to oxidation.
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 with diazomethane or the pyrolysis of the adduct of cyclohexene and dichlorocarbene.[Buchner, et al., Ber., 18, 2377 ( 1885);][For a variation: ]
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 – 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 group and Hydroxy group groups.
File:Gamma-thujaplicin.png|Hinokitiol – composed of cycloheptatriene ring, isopropyl, Carbonyl group and Hydroxy group 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 PCl
5 as the oxidant.
CHT behaves as a diene in Diels–Alder reactions, for example with
maleic anhydride:
Many
of cycloheptatriene are known, including Cr(CO)
3(C
7H
8)
and cycloheptatrienemolybdenum tricarbonyl.
Cyclooctatetraene and cycloheptatriene are used as a
Spin triplet quencher for rhodamine 6G
.
See also
