Question

I. Conjugated dienes undergo Diels-Alder reaction and form 6-membered rings. In order for this reaction to occur, the diene must be in the S-cis conformation and an alkene (dienophile) preferably with an electron-withdrawing group. EWEW EW Diene S-cis conformation Dienophile racemic product Indicate which of the following compounds can function as the diene in Diels- Alder reaction and why: doo coa 10) The rates of Diels-Alder reaction of the compounds below are compare with that of 1,3butadiene. Please explain the trend. HyC сн. CHH H.C CE faster Slower similar to butadiene

Answer 1

ans (i)

The last four compound (cyclopentadiene, 1-vinylcyclohexene, 2,4-Hexadiene and Bicyclohexene)  are function as diene because they have s-cis configuration (single-bond in cis configuration) but starting three compound does possible s-cis configuration .

Note: In Bicyclohexene each cyclohexene connect though single bond which is rotating so s-cis configuration occur.

ans (ii)

As the s-cis configuration stable it function better as diene

hence in initial starting butadiene s-cis configuration is hindering by 1,4 methyl group so s-cis configuration is less stable hence their rate is less.

2,3 methyl substituted in third number butadiene is not terminal hindered hence stable s-cis configuration so its reactivity faster than  starting two

In cyclopentadiene   s-cis configuration is most stable hence its reactivity faster.