객관식
Which of the following is the least reactive diene in a Diels-Alder reaction?
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16. Conjugated Systems
Diels-Alder Reaction
객관식
Which of the following dienes is the most reactive in a reaction?
A
(1,3-butadiene)
B
with an group at C-1 (1-methoxy-1,3-butadiene)
C
(trans,trans-1,4-diphenyl-1,3-butadiene)
D
Cyclopentadiene
검증된 단계별 안내1
Identify the key factor that influences diene reactivity in a Diels-Alder reaction: the electron density of the diene. Electron-rich dienes tend to be more reactive because they interact more effectively with the dienophile's lowest unoccupied molecular orbital (LUMO).
Examine the substituents on each diene. Electron-donating groups (EDGs), such as alkoxy groups (e.g., \( \mathrm{OCH_3} \)), increase the electron density on the diene, enhancing its reactivity. Conversely, electron-withdrawing groups or bulky substituents can decrease reactivity.
Analyze the resonance and conjugation effects. For example, a methoxy group at C-1 of 1,3-butadiene can donate electron density through resonance, stabilizing the diene's highest occupied molecular orbital (HOMO) and making it more reactive in the Diels-Alder reaction.
Consider steric effects. Bulky substituents like phenyl groups at the ends of the diene can hinder the approach of the dienophile, reducing reactivity despite any electronic effects.
Compare the dienes based on these factors: the unsubstituted 1,3-butadiene, the 1-methoxy-1,3-butadiene (with an EDG), the trans,trans-1,4-diphenyl-1,3-butadiene (with bulky phenyl groups), and cyclopentadiene (which is highly reactive due to its locked s-cis conformation). The diene with the strongest electron-donating substituent and favorable conformation will be the most reactive.
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