Textbook Question
How could the following compounds be synthesized using a Diels–Alder reaction?
a.
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16. Conjugated Systems
Diels-Alder Reaction
6:15 minutesProblem 92b
Textbook Question
How would the following substituents affect the rate of a Diels–Alder reaction?
b. an electron-donating substituent in the dienophile
Verified step by step guidance1
Understand the Diels–Alder reaction: It is a [4+2] cycloaddition reaction between a conjugated diene and a dienophile. The reaction is facilitated by electron-rich dienes and electron-deficient dienophiles.
Analyze the role of substituents: Substituents on the dienophile can influence its reactivity. Electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) have opposite effects on the electron density of the dienophile.
Consider the effect of an electron-donating substituent: An electron-donating substituent (e.g., -OH, -OR, -NH2) increases the electron density on the dienophile by donating electrons through resonance or induction.
Relate this to the reaction rate: A dienophile with increased electron density becomes less electrophilic, making it less reactive toward the electron-rich diene. This would slow down the rate of the Diels–Alder reaction.
Conclude the impact: The presence of an electron-donating substituent in the dienophile decreases the rate of the Diels–Alder reaction because it reduces the electrophilicity of the dienophile, which is essential for the reaction to proceed efficiently.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diels–Alder Reaction
The Diels–Alder reaction is a [4+2] cycloaddition reaction between a conjugated diene and a dienophile, forming a six-membered ring. This reaction is a key method in organic synthesis for constructing cyclic compounds and is characterized by its stereospecificity and regioselectivity. Understanding the mechanism and the factors influencing the reaction rate is crucial for predicting the outcomes of various substituents.
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Electron-Donating Groups (EDGs)
Electron-donating groups are substituents that increase the electron density of the molecule to which they are attached. In the context of the Diels–Alder reaction, an electron-donating substituent on the dienophile enhances its reactivity by stabilizing the transition state, making it more favorable for the reaction to occur. This increased reactivity can lead to faster reaction rates and higher yields of the desired product.
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Reaction Rate and Substituent Effects
The rate of a chemical reaction can be significantly influenced by the nature of substituents on the reactants. In the Diels–Alder reaction, substituents that either donate or withdraw electrons can alter the electron density of the diene and dienophile, affecting their reactivity. Understanding how these substituents interact with the reaction mechanism is essential for predicting the rate and efficiency of the Diels–Alder reaction.
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