Barrelene

Barrelene is a bicyclic organic compound, meaning that it is a molecule that features two fused rings. Barrelene has the chemical formula of C 8 H 8. Zimmerman first synthesized it in 1960 and named it barrelene because of its resemblance to a barrel (Figure 1). The staves are three ethylene units attached to two methine groups. It has a molar mass of of 104.15 g/mol. Barrelene is like benzene in that it has a set of 6 cyclic, overlapping p-orbitals(not planar) (Figure 2). Barrelene is hydrogenated with hydrogen gas. Figure 1 Figure 2

Triptycenes, with the alkene groups part of an arene, are related compounds. It is also a starting material for many other organic compounds such as semibullvalene.

Barrelene Reactions
Barrelene is hydrogenated with hydrogen gas and Adams' catalyst in ethanol to the fully saturated bicyclo[2.2.2]-octane. Bromination with bromine in tetrachloromethane gives a di-bromo adduct because a coupling reaction intervenes:

Epoxidation of barrelene with oxone gives the trioxatrishomobarrelene which on rearrangement with boron trifluoride (driving force:relief of strain energy ) converts into the trioxatrishomocubane:

This compound can be envisioned as a cubane with three oxygen atoms inserted into three opposite edges or as 9-crown-3 capped by two methine units. The molecule is chiral and the separate enantiomers have been isolated. Certain barrelenes have been used as a monomer in a ring opening metathesis polymerization :



The catalyst is a Fischer carbene (a //molybdenum bis-(hexafluoro-tert-butoxy) carbene catalyst//) and the long alkyl chain attached to the monomer is required for solubility. Oxidation of the polymer with DDQ affords the naphthalene pendant of poly(p-phenylene vinylene). Isopentane solutions of barrelene undergo photolytic isomerisation when acetone is added as a photosensitizer to produce semibullvalene. Prolonged irradiation results in further isomerisation to form cyclooctatetraene.


 * Barrelene** is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by H.E. Zimmerman in 1960 the name derives from the obvious resemblance with a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels-Alder adduct of benzene and acetylene. Due to its unusual molecular geometry the compound is of considerable interest to theoretical chemists. Like benzene, barrelene has a set of 6 cyclic, but not planar, overlapping p-orbitals. Because it is not possible to avoid a destabilizing overlap of opposite-sign lobes, the structure represents Mobius aromaticity.

Structure Image