객관식
Which of the following is the major product when reacts with in a Diels-Alder reaction?
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16. Conjugated Systems
Diels-Alder Reaction
객관식
Given the reaction between (1,3-butadiene) and (ethene-1,2-dione), identify the expected major product of the Diels-Alder reaction.
A
A six-membered ring with two adjacent carbonyl groups (a cyclohexene-1,2-dione)
B
A linear dione with four carbons between the carbonyl groups
C
A benzene ring
D
A five-membered ring with one carbonyl group
검증된 단계별 안내1
Step 1: Identify the diene and the dienophile in the reaction. Here, 1,3-butadiene (C\_4H\_6) acts as the diene because it has conjugated double bonds, and ethene-1,2-dione (C\_2H\_2O\_2), also known as glyoxal, acts as the dienophile because it contains electron-withdrawing carbonyl groups adjacent to the double bond.
Step 2: Recall the general mechanism of the Diels-Alder reaction, which is a [4+2] cycloaddition where the diene's 4 π-electrons and the dienophile's 2 π-electrons form a new six-membered ring in a concerted process without intermediates.
Step 3: Draw the 1,3-butadiene in the s-cis conformation to allow the ends of the diene to approach the dienophile properly, and align the ethene-1,2-dione so that its double bond is positioned to react with the diene.
Step 4: Form the new sigma bonds between the terminal carbons of the diene and the carbons of the dienophile double bond, resulting in a six-membered ring. Because the dienophile has two adjacent carbonyl groups, these will become substituents on the ring at the positions where the dienophile carbons were involved.
Step 5: Conclude that the product is a cyclohexene ring bearing two adjacent carbonyl groups (a cyclohexene-1,2-dione), which corresponds to the major product expected from this Diels-Alder reaction.
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