Textbook Question
Show how you would use Grignard syntheses to prepare the following alcohol from the indicated starting material and any other necessary reagents.
(a) octan-3-ol from hexanal, CH3(CH2)4CHO
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Ch.10 - Structure and Synthesis of Alcohols
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 10, Problem 39e
Show how you would use Grignard syntheses to prepare the following alcohol from the indicated starting material and any other necessary reagents.
(e) benzyl alcohol (Ph–CH2–OH) from bromobenzene (Ph–Br)
Verified step by step guidance1
Step 1: Begin by preparing the Grignard reagent from the starting material, bromobenzene (Ph-Br). React bromobenzene with magnesium (Mg) in an anhydrous ether solvent (e.g., diethyl ether) to form phenylmagnesium bromide (Ph-MgBr). This reaction is represented as: Ph-Br + Mg → Ph-MgBr.
Step 2: To introduce the -CH2OH group, react the Grignard reagent (Ph-MgBr) with formaldehyde (HCHO). Formaldehyde is the simplest aldehyde and will add a single carbon to the benzene ring. The reaction proceeds via nucleophilic addition, where the carbon in Ph-MgBr attacks the carbonyl carbon of formaldehyde.
Step 3: After the nucleophilic addition, the intermediate formed is a magnesium alkoxide. This intermediate has the structure Ph-CH2-O-MgBr.
Step 4: Perform an acidic workup by adding a dilute acid (e.g., HCl or H2SO4) to the reaction mixture. This step protonates the alkoxide group (-O-MgBr) to form the desired alcohol, benzyl alcohol (Ph-CH2-OH).
Step 5: Verify the product structure and ensure that the reaction conditions are anhydrous during the Grignard reagent preparation, as Grignard reagents are highly reactive with water and will decompose if exposed to moisture.
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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, typically represented as R-MgX, where R is an organic group and X is a halogen. They are highly reactive and can act as nucleophiles, allowing them to react with electrophiles to form new carbon-carbon bonds. In the context of synthesizing alcohols, Grignard reagents can react with carbonyl compounds to yield alcohols after hydrolysis.
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Carbonation of Grignard Reagents
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophile, resulting in the replacement of a leaving group. In the case of Grignard synthesis, the nucleophilic Grignard reagent attacks the electrophilic carbon in a carbon halide, leading to the formation of a new carbon-carbon bond. This mechanism is crucial for constructing complex organic molecules.
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Hydrolysis of Grignard Reagents
Hydrolysis of Grignard reagents is the process where the Grignard reagent reacts with water or an alcohol to form the corresponding alcohol and magnesium hydroxide halide. This step is essential after the nucleophilic attack, as it converts the intermediate alkoxide formed during the reaction into a stable alcohol. Understanding this step is vital for completing the synthesis of the desired alcohol product.
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Related Practice
Textbook Question
Show how you would synthesize the following alcohol from appropriate alkene.
(d)
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Textbook Question
Show how you would accomplish the following transformations. You may use any additional reagents you need.
(c)
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Textbook Question
Show how you would use Grignard syntheses to prepare the following alcohol from the indicated starting material and any other necessary reagents.
(d) 2-cyclohexylethanol from bromocyclohexane
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Textbook Question
Show how you would use Grignard syntheses to prepare the following alcohol from the indicated starting material and any other necessary reagents.
(g) cyclopentylphenylmethanol from benzaldehyde (Ph–CHO)
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Textbook Question
Show how you would accomplish the following transformations. You may use any additional reagents you need.
(b)
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