Textbook Question
Draw the mechanism for the last step in the Kiliani-Fischer synthesis.
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Ch. 20 - Carboxylic Acids
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 20, Problem 44e,f
Two of the methods for converting alkyl halides to carboxylic acids are covered in Sections 20-8B and 20-8C. One is formation of a Grignard reagent followed by addition of carbon dioxide and then dilute acid. The other is substitution by cyanide ion, followed by hydrolysis of the resulting nitrile. For each of the following conversions, decide whether either or both of these methods would work, and explain why. Show the reactions you would use.
(e) 
(f) 
Verified step by step guidance1
Step 1: Analyze the given alkyl halides. The first structure is bromocyclopentane, and the second structure is 2-(bromomethyl)cyclopentanol. Both need to be converted into carboxylic acids.
Step 2: For bromocyclopentane, the Grignard reagent method can be applied. First, react bromocyclopentane with magnesium in dry ether to form cyclopentylmagnesium bromide. Then, add carbon dioxide (CO₂) to form the magnesium carboxylate intermediate. Finally, hydrolyze the intermediate with dilute acid to yield cyclopentane carboxylic acid.
Step 3: For bromocyclopentane, the cyanide substitution method can also be applied. React bromocyclopentane with sodium cyanide (NaCN) in an aprotic solvent like DMSO to form cyclopentyl nitrile. Then, hydrolyze the nitrile under acidic or basic conditions to yield cyclopentane carboxylic acid.
Step 4: For 2-(bromomethyl)cyclopentanol, the Grignard reagent method is not suitable because the hydroxyl group (-OH) can interfere with the formation of the Grignard reagent by reacting with magnesium. Thus, this method is not recommended for this compound.
Step 5: For 2-(bromomethyl)cyclopentanol, the cyanide substitution method can be applied. React 2-(bromomethyl)cyclopentanol with sodium cyanide (NaCN) in an aprotic solvent to form 2-(cyanomethyl)cyclopentanol. Then, hydrolyze the nitrile under acidic or basic conditions to yield 2-(carboxymethyl)cyclopentanol.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Grignard Reagents
Grignard reagents are organomagnesium compounds formed by reacting alkyl or aryl halides with magnesium metal. They are highly reactive nucleophiles that can add to carbonyl compounds, such as carbon dioxide, to form carboxylic acids upon subsequent acid workup. Understanding their formation and reactivity is crucial for converting alkyl halides to carboxylic acids.
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Carbonation of Grignard Reagents
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile replaces a leaving group in a molecule. In the context of converting alkyl halides to carboxylic acids, cyanide ion acts as a nucleophile, substituting the halide to form a nitrile, which can then be hydrolyzed to yield the desired carboxylic acid. This mechanism is essential for understanding the reactivity of alkyl halides.
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Hydrolysis of Nitriles
Hydrolysis of nitriles involves the reaction of nitriles with water, often in the presence of an acid or base, to convert them into carboxylic acids. This process is significant in organic synthesis as it allows for the transformation of a nitrile, formed from a nucleophilic substitution reaction, into a carboxylic acid. Recognizing the conditions and mechanisms of hydrolysis is vital for successful conversions in organic reactions.
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Related Practice
Textbook Question
Two of the methods for converting alkyl halides to carboxylic acids are covered in Sections 20-8B and 20-8C. One is formation of a Grignard reagent followed by addition of carbon dioxide and then dilute acid. The other is substitution by cyanide ion, followed by hydrolysis of the resulting nitrile. For each of the following conversions, decide whether either or both of these methods would work, and explain why. Show the reactions you would use.
(a)
(b)
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Textbook Question
Peroxyacetic acid (bp = 105 °C) has a lower boiling point than acetic acid (bp = 118 °C), even though peroxyacetic acid has a higher molecular weight. Explain why peroxyacetic acid is more volatile than acetic acid.
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Textbook Question
In the presence of a trace of acid, δ-hydroxyvaleric acid forms a cyclic ester (lactone).
(a) Give the structure of the lactone, called δ-valerolactone.
(b) Propose a mechanism for the formation of δ-valerolactone.
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