1. Give an explanation for the following: a. Cyclopentadiene dimerizes more read
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Question
1. Give an explanation for the following: a. Cyclopentadiene dimerizes more readily than acyclic dienes.
b. Cyclopentadiene reacts more rapidly with maleic anhydride than with another cyclopentadiene molecule.
c. Commercial cyclopentadiene cannot be used as a conjugated diene in a Diels-Alder reaction.
d. The distillate of the fractional distillation is collected in ice.
e. Cyclopentadiene is added to a cool solution of maleic anhydride.
Why is Maleic anhydride a better dienophile for Diels-Alder reaction?
What conformation of the diene is favorable for Diels-Alder reaction?
Explanation / Answer
a. The acyclic dienes can react with dienophile to give diels-Alder reaction when it adopts the s-cis conformation. However, in cyclopentadiene, the two double bonds are constrained or locked into the s-cis form, hence are more reactive.
b. Diels-Alder cycloaddition reactions proceed rapidly when the diene is electron rich and the dienophile is electron poor.
An electron rich cyclopentadiene acts as a 4 -electron diene and undergoes slow cycloaddition with another molecule of itself which acts as a 2 -electron dieneophile to form dicyclopentadiene.
On the other hand, cyclopentadiene reacts rapidly with maleic anhydride, which is an electron poor dieneophile reacts to give an endo Diels-Alder adduct.
c. Commercial cyclopentadiene cannot be used as a conjugated diene in a Diels-Alder reaction because it undergoes dimerization at 25 oC to produce dicyclopentadiene.
d. The distillate of the fractional distillation is collected in ice so that the volatile cyclopentadiene is prevented from the formation of the dicyclopentadiene.
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