Textbook Question
Show how you would accomplish the following syntheses. You may use whatever additional reagents you need.
(b)
21. Aldehydes and Ketones: Nucleophilic Addition
Acetal Protecting Group
5:11 minutesProblem 68a
Textbook Question
One of these reacts with dilute aqueous acid and the other does not. Give a mechanism for the one that reacts, and show why this mechanism does not work for the other one.
(a) 
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Identify the functional groups present in both compounds. Typically, compounds that react with dilute aqueous acid contain functional groups like epoxides, esters, or amides that can be protonated.
For the compound that reacts, propose a mechanism starting with the protonation of the functional group by the acid. This often involves the lone pair of electrons on the oxygen or nitrogen atom attacking the hydrogen ion (H⁺) from the acid.
Once protonated, the functional group becomes more electrophilic, making it susceptible to nucleophilic attack. Identify the nucleophile in the reaction, which could be water or another molecule present in the solution.
Illustrate the nucleophilic attack on the electrophilic center, leading to the opening of a ring (if applicable) or the formation of a new bond. This step often involves the movement of electrons and the breaking of a bond.
For the compound that does not react, explain why the mechanism fails. This could be due to the absence of a suitable electrophilic center, steric hindrance, or the lack of a good leaving group, preventing the reaction from proceeding.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Reactions
Acid-base reactions involve the transfer of protons (H+) between reactants. In organic chemistry, understanding how different functional groups interact with acids is crucial. For example, alcohols can react with acids to form alkyl halides through protonation, while other groups may not exhibit this behavior due to their structural characteristics.
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The Lewis definition of acids and bases.
Reaction Mechanisms
A reaction mechanism describes the step-by-step process by which reactants transform into products. It includes details about bond breaking and forming, intermediates, and transition states. For the compound that reacts with dilute aqueous acid, a detailed mechanism will illustrate how the reaction proceeds, while the other compound's mechanism will highlight the absence of such steps.
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Functional Group Reactivity
Different functional groups exhibit varying reactivities based on their electronic and steric properties. For instance, alkenes and alkynes can undergo electrophilic addition reactions, while saturated hydrocarbons typically do not react with dilute acids. Identifying the functional groups present in the compounds is essential to predict their behavior in acid reactions.
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