Predict the product of the following reductions.
(a)

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Identify the functional group present in the starting material. In this case, the compound is a lactone, which is a cyclic ester.

Recognize the reducing agent used in the reaction. Lithium aluminum hydride (LiAlH₄) is a strong reducing agent capable of reducing esters to alcohols.

Understand the mechanism of reduction. LiAlH₄ will donate hydride ions (H⁻) to the carbonyl carbon of the ester, breaking the C=O bond and forming an alkoxide intermediate.

Consider the role of the second step, which involves an acid quench (H₃O⁺). This step protonates the alkoxide intermediate, resulting in the formation of an alcohol.

Predict the final product. The reduction of the lactone will open the ring and convert the ester into a diol, specifically a 1,5-diol, due to the original five-membered ring structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reduction Reactions

Reduction reactions in organic chemistry involve the gain of electrons or hydrogen, or the loss of oxygen by a molecule. These reactions typically convert carbonyl compounds, such as aldehydes and ketones, into alcohols. Understanding the type of reduction (e.g., catalytic hydrogenation, metal hydride reduction) is crucial for predicting the products formed.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Recognizing the functional groups present in the reactants is essential for predicting the outcome of reduction reactions, as different groups react differently under reducing conditions.

Stereochemistry

Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In reduction reactions, the stereochemistry of the starting material can influence the stereochemical outcome of the product, especially in cases involving chiral centers. Understanding stereochemical principles is vital for accurately predicting the products of reductions.

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You might expect that aldehydes and ketones could undergo the addition/elimination mechanism. With strong nucleophiles, however, nucleophilic addition is the only outcome. Why?

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Predict the product of the following reductions.

(d)

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How would you expect the IR and ¹H NMR spectra for propanamide and N,N-diethylpropanamide to differ?

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