1,6-Methano(10)annulene

The correct title of this article is 1,6-Methano[10]annulene. The substitution of any brackets is due to technical restrictions.

1,6-Methano[10]annulene (also known as 1,6-methanonaphthalene or homonaphthalene) is an aromatic hydrocarbon with chemical formula C₁₁H₁₀. It was the first stable aromatic compound based on the cyclodecapentaene system to be discovered.

1,6-Methano[10]annulene

Names
Preferred IUPAC name Bicyclo[4.4.1]undeca-1,3,5,7,9-pentaene
Identifiers
CAS Number	2443-46-1
3D model (JSmol)	Interactive image
ChemSpider	121264
PubChem CID	137603
CompTox Dashboard (EPA)	DTXSID40179188
InChI InChI=1S/C11H10/c1-2-6-11-8-4-3-7-10(5-1)9-11/h1-8H,9H2 Key: OORRQYZWSVJKSO-UHFFFAOYSA-N InChI=1/C11H10/c1-2-6-11-8-4-3-7-10(5-1)9-11/h1-8H,9H2 Key: OORRQYZWSVJKSO-UHFFFAOYAC
SMILES c1ccc2ccccc(c1)C2
Properties
Chemical formula	C11H10
Molar mass	142.201 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

The classical organic synthesis of this compound starts with Birch reduction of naphthalene to isotetralin, which adds dichlorocarbene (prepared in situ from chloroform and potassium tert-butoxide) to form a transannular cyclopropane ring. A second reduction then removes the chloride substituents. Finally, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation removes the central transannular bond and dehydrogenates unto aromaticity.^[1]

Aromaticity

It is analogous to cyclodecapentaene ([10]annulene), but with two hydrogen atoms replaced by a transannular methylene bridge (−CH₂−). Consequently, it obeys Hückel's rule (n = 2) and despite the distortion from planarity introduced by the methylene bridge, the compound is aromatic.^[2][3] In fact, when prepared by Vogel in the 1960s^[4][5] it was the first stable aromatic cyclodecapentaene to be discovered.^[3] Its aromaticity is confirmed by two main pieces of evidence. Firstly, the similarity in carbon-carbon bond lengths as measured by x-ray crystallography is inconsistent with alternating single and double bonds. The actual structure is better considered as a pair of resonance hybrids (like the Kekulé structures of benzene) rather than as having alternating single and double bonds.

Secondly, its ¹H NMR spectrum displays influence of the diamagnetic ring current which is characteristic of aromatic compounds. The peripheral protons around the ring are deshielded while the methylene bridge nuclei are strongly shielded.^[2][3]

Its resonance energy is smaller than that of naphthalene.^[6]

Possible applications

Homonaphthalene has been used in the production of conductive polymers.^[7]

See also

• Homoaromaticity
• Cyclodecapentaene
• 1,5-Methano[10]annulene