Question

How can you tell if Diels- Alder reaction has gone all the way to completion or not?

Answer 1

Depending upon the substrate one may use the method to check progress and thus completion of a diels alder reaction. A diene and a dienophile usually are conjugated and show certain lambda-max in UV spectrum. As the reaction gets completed the conjugation of the diene and dienophile are destroyed and we should get a less colored or clear solution. Another more prominent method of reaction progress measurement is by thin layer chromatographic analysis. Mostly the mobile phase employed for running tlc would be mixture of hexane-ethylacetate. Silica is used as a support. tlc of reaction mixture (aliquot diluted with proper solvent) along with substrates and the expected product If available is spoted on the plate. Substrates are easily visible in UV light, products will be faint. Once the substrate spot in the reaction mixture disappears it shows completion of diels alder reaction.