Textbook Question
Show how you would convert propan-1-ol to the following compounds using tosylate intermediates. You may use whatever additional reagents are needed.
c. CH3CH2CH2OCH2CH3, ethyl proyl ether
d. CH3CH2CH2CN, butyronitrile
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Ch.11 - Reactions 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 11, Problem 12a
Propose a mechanism for the reaction of
(a) 1-methylcyclohexanol with HBr to form 1-bromo-1-methylcyclohexane.
Verified step by step guidance1
Step 1: Protonation of the alcohol group - The hydroxyl group (-OH) in 1-methylcyclohexanol is a poor leaving group. To make it a better leaving group, it is protonated by HBr, forming water (H2O) as a better leaving group. This step involves the transfer of a proton (H⁺) from HBr to the oxygen atom of the hydroxyl group.
Step 2: Formation of a carbocation intermediate - After protonation, the water molecule leaves, resulting in the formation of a carbocation at the carbon atom that was originally bonded to the hydroxyl group. Since the hydroxyl group is attached to a tertiary carbon (1-methylcyclohexanol is a tertiary alcohol), the resulting carbocation is a tertiary carbocation, which is relatively stable due to hyperconjugation and inductive effects.
Step 3: Nucleophilic attack by bromide ion - The bromide ion (Br⁻), which is generated from the dissociation of HBr, acts as a nucleophile and attacks the positively charged carbocation. This step involves the formation of a new C-Br bond, resulting in the product 1-bromo-1-methylcyclohexane.
Step 4: Verify the stereochemistry - Since the reaction proceeds through a carbocation intermediate, the product may exhibit racemization if the carbon center is chiral. However, in this case, the product is not chiral, so no stereochemical considerations are necessary.
Step 5: Summarize the mechanism - The overall reaction involves three key steps: protonation of the alcohol group, formation of a carbocation intermediate, and nucleophilic attack by the bromide ion. The final product is 1-bromo-1-methylcyclohexane.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alcohol Reactivity
Alcohols, such as 1-methylcyclohexanol, can undergo nucleophilic substitution reactions. In the presence of strong acids like HBr, the hydroxyl (-OH) group is protonated, converting it into a better leaving group (water). This transformation is crucial for facilitating the subsequent substitution reaction where the bromide ion replaces the -OH group.
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Nucleophilic Substitution Mechanism
The reaction mechanism for converting alcohols to alkyl halides typically follows an SN1 or SN2 pathway. In this case, the reaction likely proceeds via an SN1 mechanism due to the stability of the carbocation formed after the leaving group departs. The formation of a stable tertiary or secondary carbocation allows for the rapid attack by the bromide ion, leading to the final product.
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Carbocation Stability
Carbocation stability is a key factor in determining the pathway of nucleophilic substitution reactions. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects from surrounding alkyl groups. In the case of 1-methylcyclohexanol, the formation of a stable carbocation intermediate is essential for the efficient conversion to 1-bromo-1-methylcyclohexane.
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Related Practice
Textbook Question
Show how you would use a simple chemical test to distinguish between the following pairs of compounds. Tell what you would observe with each compound.
(d) allyl alcohol and propan-1-ol
(e) butan-2-one and tert-butyl alcohol
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Textbook Question
Predict the products of the following reactions.
(c) 1-methylcyclohexanol + H2SO4, heat
(d) product of (c) + H2, Pt
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Textbook Question
Predict the products of the following reactions.
(a) cyclohexylmethanol + TsCl/pyridine
(b) product of (a) + LiAlH4
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Textbook Question
Neopentyl alcohol, (CH3)3CCH2OH, reacts with concentrated HBr to give 2-bromo-2-methylbutane, a rearranged product. Propose a mechanism for the formation of this product.
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Textbook Question
The reaction of tert-butyl alcohol with concentrated HCl goes by the SN1 mechanism. Write a mechanism for this reaction.
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