Isotoluene
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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]
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/mole less stable.
The isomerization of p-isotoluene to toluene takes place at 100°C in benzene with bimolecular reaction kinetics by a 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 is been researched in connection with the mechanism of initiator-free polymerization of polystyrene.
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[edit] References
- ^ Radical production from the interaction of closed-shell molecules. 10. Chemistry of methylenecyclohexadiene and the thermal polymerization of styrene W. David Graham, John Glass Green, and William A. Pryor J. Org. Chem.; 1979; 44(6) pp 907 - 914; DOI:10.1021/jo01320a003.
- ^ Bimolecular reactions of 3-methylene-1,4-cyclohexadiene (p-isotoluene), 5-methylene-1,3-cyclohexadiene (o-isotoluene), 1-methylene-1,4-dihydronaphthalene (benzo-p-isotoluene), and 9-methylene-9,10-dihydroanthracene (dibenzo-p-isotoluene) Joseph J. Gajewski and Andrea M. Gortva J. Org. Chem.; 1989; 54(2) pp 373 - 378; DOI:10.1021/jo00263a021
