Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - Using HX

Organic Chemistry

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - Using HX

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5:20 minutes

Problem 55a

Textbook Question

Propose mechanisms for the following reactions. In most cases, more products are formed than are shown here. You only need to explain the formation of the products shown, however.
(a)

Verified step by step guidance

Step 1: Recognize the reaction conditions. The presence of HCl and ZnCl₂ indicates that this is a Lucas test reaction, which involves the conversion of alcohols to alkyl halides via an SN1 mechanism. ZnCl₂ acts as a Lewis acid, enhancing the reactivity of the alcohol.

Step 2: Protonation of the alcohol group. The hydroxyl group (-OH) on the cyclohexylmethanol is protonated by HCl, forming water as a leaving group. This step increases the electrophilicity of the carbon attached to the hydroxyl group.

Step 3: Formation of a carbocation intermediate. After the water molecule leaves, a carbocation is formed at the benzylic position (CH₂ group attached to the cyclohexane ring). This carbocation is relatively stable due to hyperconjugation and inductive effects from the cyclohexane ring.

Step 4: Rearrangement of the carbocation. A hydride shift occurs from the cyclohexane ring to the carbocation, resulting in a more stable secondary carbocation directly on the cyclohexane ring. This rearrangement explains the formation of the minor product.

Step 5: Nucleophilic attack by chloride ion. The chloride ion (Cl⁻) from HCl attacks the secondary carbocation, forming the final product, chlorocyclohexane. This product is labeled as the minor product because the primary product would involve substitution at the original benzylic position without rearrangement.

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Key Concepts

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

Reaction Mechanisms

A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level. It outlines the sequence of elementary steps, including bond breaking and formation, that lead to the transformation of reactants into products. Understanding mechanisms is crucial for predicting the products of reactions and for explaining why certain pathways are favored over others.

Types of Organic Reactions

Organic reactions can be classified into several types, including substitution, addition, elimination, and rearrangement reactions. Each type has distinct characteristics and mechanisms. Recognizing the type of reaction helps in predicting the behavior of reactants and the nature of the products formed, which is essential for proposing accurate mechanisms.

Stability of Intermediates

The stability of reaction intermediates, such as carbocations, carbanions, and free radicals, plays a significant role in determining the pathway of a reaction. More stable intermediates are generally formed preferentially, influencing the overall reaction mechanism and the products generated. Understanding the factors that affect stability, such as resonance and inductive effects, is vital for accurately proposing mechanisms.

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Related Practice

Textbook Question

Predict the product of the following reactions.

(c)

Textbook Question

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (vii) HCl; (viii) HBr. If no reaction occurs, write 'no reaction.'

(a)

Textbook Question

Predict the product of the following reactions.

(b)

Textbook Question

Suggest the appropriate reagents to carry out the following transformations.

(d)

Textbook Question

Propose a mechanism for the reaction of

(a) 1-methylcyclohexanol with HBr to form 1-bromo-1-methylcyclohexane.

Textbook Question

When cis-2-methylcyclohexanol reacts with the Lucas reagent, the major product is 1-chloro-1-methylcyclohexane. Propose a mechanism to explain the formation of this product.

Textbook Question

(a) The reaction of butan-2-ol with concentrated aqueous HBr goes with partial racemization, giving more inversion than retention of configuration. Propose a mechanism that accounts for racemization with excess inversion.

Textbook Question

(b) Under the same conditions, an optically active sample of trans-2-bromocyclopentanol reacts with concentrated aqueous HBr to give an optically inactive product, (racemic) trans-1,2-dibromocyclopentane. Propose a mechanism to show how this reaction goes with apparently complete retention of configuration, yet with racemization. (Hint: Draw out the mechanism of the reaction of cyclopentene with Br₂ in water to give the starting material, trans-2- bromocyclopentanol. Consider how parts of this mechanism might be involved in the reaction with HBr.)

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Propose mechanisms for the following reactions. In most cases, more products are formed than are shown here. You only need to explain the formation of the products shown, however.(a)

Key Concepts

Reaction Mechanisms

Types of Organic Reactions

Stability of Intermediates

Watch next

Propose mechanisms for the following reactions. In most cases, more products are formed than are shown here. You only need to explain the formation of the products shown, however.
(a)