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1. An aldol reaction begins with addition of a catalytic amount of base to an aldehyde or ketone. Write the first step (formation of an enolate) of the reaction when a catalytic amount of NaOH is added to acetaldehyde. 11 Bose

1. An aldol reaction begins with addition of a catalytic amount of base to an aldehyde or ketone. Write the first step (formation of an enolate) of the reaction when a catalytic amount of NaOH is added to acetaldehyde. 11 Bose

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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### Aldol Addition Reaction and Mechanisms #### 1. Formation of Enolate An aldol reaction begins with the addition of a catalytic amount of base to an aldehyde or ketone. Below are the steps for the reaction of acetaldehyde with a catalytic amount of NaOH. - The reaction starts with the deprotonation of acetaldehyde at the alpha position, forming an enolate ion. This enolate ion acts as a nucleophile. The diagram shows: - Acetaldehyde with a base attacking the alpha hydrogen to form the enolate ion. #### 2. Formation of β-Hydroxyaldehyde Continue the reaction by combining the enolate with an unaffected molecule of acetaldehyde to form an alkoxide. A subsequent reaction with water yields a β-hydroxyaldehyde. - The enolate ion attacks the carbonyl carbon of another acetaldehyde molecule, forming a bond and generating an alkoxide intermediate. - The alkoxide is then protonated by water, forming β-hydroxyaldehyde. - The diagrams illustrate the enolate attacking the carbonyl carbon, followed by the formation of the β-hydroxyaldehyde. #### 3. Retro-Aldol Reaction The overall aldol reaction is reversible. This means the β-hydroxyaldehyde can be converted back into two molecules of the original aldehyde. This reverse process is called a retro-aldol reaction. - The β-hydroxyaldehyde loses a hydroxide ion, forming back the enolate and the original aldehyde. - Use pKₐ values to explain the reversible nature of this process. - The accompanying diagrams display the retro-aldol mechanism, showing decomposition into original aldehyde units. #### 4. Mechanism for Butanone Reaction Write the mechanism for the reaction of butanone with catalytic aqueous NaOH. Show each step with a reversible reaction arrow. - Follow a similar process: - Formation of the enolate. - Reaction of the enolate with the ketone to form a diol. - Diol conversion back to the original ketone. - Diagrams are provided to depict each mechanistic step, highlighting reversibility. This explanation and the accompanying diagrams serve as an educational guide to understanding the mechanism and reversibility of the aldol and retro-aldol reactions in organic chemistry.
Transcribed Image Text:### Aldol Addition Reaction and Mechanisms #### 1. Formation of Enolate An aldol reaction begins with the addition of a catalytic amount of base to an aldehyde or ketone. Below are the steps for the reaction of acetaldehyde with a catalytic amount of NaOH. - The reaction starts with the deprotonation of acetaldehyde at the alpha position, forming an enolate ion. This enolate ion acts as a nucleophile. The diagram shows: - Acetaldehyde with a base attacking the alpha hydrogen to form the enolate ion. #### 2. Formation of β-Hydroxyaldehyde Continue the reaction by combining the enolate with an unaffected molecule of acetaldehyde to form an alkoxide. A subsequent reaction with water yields a β-hydroxyaldehyde. - The enolate ion attacks the carbonyl carbon of another acetaldehyde molecule, forming a bond and generating an alkoxide intermediate. - The alkoxide is then protonated by water, forming β-hydroxyaldehyde. - The diagrams illustrate the enolate attacking the carbonyl carbon, followed by the formation of the β-hydroxyaldehyde. #### 3. Retro-Aldol Reaction The overall aldol reaction is reversible. This means the β-hydroxyaldehyde can be converted back into two molecules of the original aldehyde. This reverse process is called a retro-aldol reaction. - The β-hydroxyaldehyde loses a hydroxide ion, forming back the enolate and the original aldehyde. - Use pKₐ values to explain the reversible nature of this process. - The accompanying diagrams display the retro-aldol mechanism, showing decomposition into original aldehyde units. #### 4. Mechanism for Butanone Reaction Write the mechanism for the reaction of butanone with catalytic aqueous NaOH. Show each step with a reversible reaction arrow. - Follow a similar process: - Formation of the enolate. - Reaction of the enolate with the ketone to form a diol. - Diol conversion back to the original ketone. - Diagrams are provided to depict each mechanistic step, highlighting reversibility. This explanation and the accompanying diagrams serve as an educational guide to understanding the mechanism and reversibility of the aldol and retro-aldol reactions in organic chemistry.
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