Textbook Question
Propose a mechanism for each cyanohydrin synthesis just shown.
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Ch. 18 - Ketones and Aldehydes
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 18, Problem 13a
Propose mechanisms for
(a) the acid-catalyzed hydration of chloral to form chloral hydrate.
Verified step by step guidance1
Identify the reactants and products: The reactant is chloral (CCl₃CHO), and the product is chloral hydrate (CCl₃CH(OH)₂). This reaction involves the addition of water to the carbonyl group of chloral under acidic conditions.
Step 1: Protonation of the carbonyl group. The acid catalyst donates a proton (H⁺) to the oxygen atom of the carbonyl group in chloral, increasing the electrophilicity of the carbonyl carbon. This forms a protonated intermediate.
Step 2: Nucleophilic attack by water. A water molecule acts as a nucleophile and attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate. This step introduces an -OH group to the carbon.
Step 3: Deprotonation of the intermediate. The tetrahedral intermediate formed in the previous step undergoes deprotonation (loss of H⁺) to stabilize the structure, resulting in the formation of a geminal diol (chloral hydrate).
Step 4: Regeneration of the acid catalyst. The proton (H⁺) lost during the deprotonation step is returned to the solution, ensuring that the acid catalyst is regenerated and the reaction can proceed catalytically.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Catalyzed Hydration
Acid-catalyzed hydration is a chemical reaction where water is added to a compound in the presence of an acid, which acts as a catalyst. The acid protonates the carbonyl oxygen of the compound, increasing its electrophilicity and facilitating the nucleophilic attack by water. This process is crucial in converting carbonyl compounds into their corresponding alcohols or hydrates.
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Acid-catalyzed hydration mechanism
Chloral and Chloral Hydrate
Chloral is an organic compound with the formula CCl3CHO, characterized by its carbonyl group. When chloral undergoes hydration, it forms chloral hydrate, a stable compound used in various applications, including as a sedative. Understanding the structure and reactivity of chloral is essential for proposing the hydration mechanism.
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Mechanism of Nucleophilic Addition
The mechanism of nucleophilic addition involves the attack of a nucleophile, such as water, on an electrophilic center, typically a carbon atom in a carbonyl group. This reaction proceeds through the formation of a tetrahedral intermediate, which can then collapse to yield the final product. Recognizing this mechanism is vital for understanding how chloral is converted to chloral hydrate.
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Related Practice
Textbook Question
Sodium triacetoxyborohydride, NaBH(OAc)3, is a mild reducing agent that reduces aldehydes much more quickly than ketones. It can be used to reduce aldehydes in the presence of ketones, such as in the following reaction:
(b) Propose a mechanism for the reduction of an aldehyde by sodium triacetoxyborohydride.
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Textbook Question
Show how you would accomplish the following syntheses.
(a) acetophenone → acetophenone cyanohydrin
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Textbook Question
Propose mechanisms for
(b) the base-catalyzed hydration of acetone to form acetone hydrate.
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Textbook Question
Show how you would accomplish the following synthetic conversions. You may use any additional reagents and solvents you need.
(d)
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Textbook Question
Sodium triacetoxyborohydride, NaBH(OAc)3, is a mild reducing agent that reduces aldehydes much more quickly than ketones. It can be used to reduce aldehydes in the presence of ketones, such as in the following reaction:
(a) Draw a complete Lewis structure for sodium triacetoxyborohydride.
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