Ch. 21 - Conjugated Systems 1: Stability and Addition Reactions

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 21 - Conjugated Systems 1: Stability and Addition Reactions

Problema 36g,h,i

Capitolo 20, Problema 36g,h,i

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?
(g)
(h)
(i)

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Identify the type of nucleophile: Determine whether the nucleophile is a strong or weak nucleophile. Strong nucleophiles tend to favor 1,2-addition, while weak nucleophiles often favor 1,4-addition.

Analyze the electrophile: Consider the structure of the electrophile, particularly if it is an α,β-unsaturated carbonyl compound. This will help determine the possible sites for nucleophilic attack.

Consider the reaction conditions: The conditions under which the reaction is carried out (e.g., temperature, solvent) can influence whether 1,2- or 1,4-addition is favored.

Evaluate the stability of intermediates: 1,4-addition often leads to more stable intermediates, such as enolates or enols, which can be a deciding factor in the reaction pathway.

Predict the outcome: Based on the analysis of the nucleophile, electrophile, and reaction conditions, predict whether 1,2- or 1,4-addition is more likely to occur for each nucleophile.

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Nucleophiles

Nucleophiles are species that donate an electron pair to form a chemical bond in reaction mechanisms. They are typically negatively charged or neutral molecules with lone pairs of electrons. Understanding the nature of nucleophiles, such as their charge, size, and electron density, is crucial for predicting their behavior in addition reactions.

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Nucleophilic Addition

1,2-Addition

1,2-Addition, also known as direct addition, occurs when a nucleophile adds to the carbon atom directly adjacent to the carbonyl group in an α,β-unsaturated carbonyl compound. This type of addition is favored by strong, small nucleophiles and results in the formation of a new bond at the carbonyl carbon, often leading to a more stable product in kinetic terms.

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09:23

1,2 vs 1,4 Addition

1,4-Addition

1,4-Addition, or conjugate addition, involves the nucleophile adding to the β-carbon of an α,β-unsaturated carbonyl compound. This pathway is typically favored by weaker, larger nucleophiles and results in the formation of a more stable product in thermodynamic terms. Understanding the conditions and nucleophile characteristics that favor 1,4-addition is essential for predicting reaction outcomes.

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09:23

1,2 vs 1,4 Addition

Pratica correlata

Domanda del libro di testo

Predict the product of the following reactions.

(b)

585

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Domanda del libro di testo

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?

(a)

(b)

1010

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Domanda del libro di testo

a. Could a nucleophile ever add to C₃?

b. Why or why not?

1004

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Domanda del libro di testo

Whereas stabilized enolates do 1,4-addition, unstabilized (normal) enolates can do both 1,2- and 1,4-addition depending on the situation. Why might this be?

789

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Domanda del libro di testo

Predict the product of the following reactions.

(a)

606

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Domanda del libro di testo

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?

(d)

(e)

(f)