Identification of a Conjugated Diene from Eucalyptus Oil

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Identification of a Conjugated Diene from Eucalyptus Oil

When two carbon-carbon double bonds are positioned next to one another, a conjugated diene is formed. Conjugated dienes undergo a cycloaddition reaction with certain double bonds to afford cyclohexenes and related compounds. The reaction is named Diels-Alder. The Diels-Alder reaction is between 1,3-butadiene and ethylene to produce cyclohexene + dienedienophile. The mechanism of the Diels-Alder reaction is classified as a [4+2] cycloaddition reaction, because one reactant (the diene), contributes four carbon atoms and the other reactant (the dienophile) contributes two carbon atoms to the six membered ring of the resulting cyclic compound (the adduct). As mentioned with the reaction of 1,3-butadiene and ethene, the diene must be able to exist  in an s-cis conformation, in which the carbon atoms that bond to the dienophile are on the same side of the C-C single bond. Concerning the stereochemistry of the product, the Diels-Alder reaction is stereo selective, usually yielding only one of several possible stereoisomer. The addition of maleic anhydride to a diene yields entirely the endo product in which the bulkier parts of the dienophile are closer to the carbon-carbon double bond.Dienes and trienes occur in the essential oils of a number of plants and contribute to the flavors and aromas of certain plants. Most conjugated dienes can form Diels-Alder with maleic anhydride.Trienes such as β-Myrcene (C10H16) may also form such adducts if at least two of their double bonds are conjugated. The IR, melting point, and NMR should be able to identify the two bands which arise from the carbonyl stretching modes and also identify the diene found in eucalyptus oil. 

• Dissolve 5.00g of eucalyptus oil in 10ml of anhydrous diethyl ether • Add calculated amount of powered maleic anhydrous-2.81grams • Heat the reaction mixture under gentle reflux for 45min • Transfer the...
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