Isotoluene

The Isotoluenes in organic chemistry are the non-aromatic toluene isomers with an exocyclic double bond. They are of some academic interest in relation to aromaticity and isomerization mechanisms^[1][2]

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The three basic isotoluenes are ortho-isotoluene or 5-methylene-1,3-cyclohexadiene. 1, para-isotoluene 2 and meta-isotoluene 3. One more isomer is the bicyclic compound 5-methylenebicyclo[2.2.0] hexene 4.

The o- and p-isotoluenes easily isomerize to toluene, a reaction obviously driven by aromatic stabilization. It is estimated that these compounds are 23 kcal/mol less stable.

The isomerization of p-isotoluene to toluene takes place at 100 °C in benzene with bimolecular reaction kinetics by an intermolecular free radical reaction. Other dimer radical reaction products are formed as well.

The ortho isomer is found to isomerize at 60°C also in a second order reaction in benzene. The proposed reaction mechanism is a concerted intermolecular ene reaction. The reaction product is either toluene or a mixture of dimerized ene reaction products depending on the exact reaction conditions.

Ortho isotoluene has been researched in connection with the mechanism of initiator-free polymerization of polystyrene.

See also

• Pentacene

References