Consider the Diels–Alder reaction of cyclopentadiene with p‑benzoquinone. Diels-Alder reaction between cyclopentadiene and p-benzoquinone Select the correct statement about the stoichiometry of this reaction.

A. Multiple molar equivalents of cyclopentadiene and p‑benzoquinone react to form a long polymer chain.

B. One molar equivalent of p‑benzoquinone can react with only one molar equivalent of cyclopentadiene.

C. Two molar equivalents of p‑benzoquinone can react with one molar equivalent of cyclopentadiene.

D. Two molar equivalents of cyclopentadiene can react with one molar equivalent of p‑benzoquinone.

The answer is (D) Two molar equivalents of cyclopentadiene can react with one molar equivalent of p‑benzoquinone.

Explanation:

The reaction between p-benzoquinone and cyclopentadiene is a 1,4-cyclo-addition reaction, will follow the general 4n+2 π electrons rule  of reaction between a dienophile and a diene.

Hence, two moles of cyclopentadiene added to p-benzoquinone will result in two possible isomers of cis endo and exo adducts (open and closed rings).  

Only reaction conditions can be varied to effect yield increase.

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as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.