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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3:31 minutes

Problem 17

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.

Verified step by step guidance

Step 1: Understand the Lucas reagent reaction. The Lucas reagent is a mixture of concentrated hydrochloric acid (HCl) and zinc chloride (ZnCl₂). It is used to convert alcohols into alkyl chlorides via an SN1 or SN2 mechanism, depending on the structure of the alcohol. Tertiary alcohols typically undergo an SN1 mechanism due to the stability of the carbocation intermediate.

Step 2: Analyze the structure of cis-2-methylcyclohexanol. The hydroxyl (-OH) group is attached to a secondary carbon, and the molecule has a methyl group on the adjacent carbon. This secondary alcohol is likely to undergo an SN1 mechanism because the resulting carbocation can be stabilized by hyperconjugation and inductive effects from the methyl group.

Step 3: Protonation of the hydroxyl group. In the presence of the Lucas reagent, the hydroxyl group is protonated by HCl, forming water as a leaving group. This step increases the electrophilicity of the carbon attached to the hydroxyl group, making it more susceptible to nucleophilic attack.

Step 4: Formation of the carbocation intermediate. After the water molecule leaves, a carbocation is formed at the secondary carbon. This carbocation is stabilized by the adjacent methyl group through hyperconjugation and inductive effects. The stability of the carbocation is crucial for the SN1 mechanism.

Step 5: Nucleophilic attack by chloride ion. The chloride ion (Cl⁻) from HCl acts as a nucleophile and attacks the carbocation, forming 1-chloro-1-methylcyclohexane as the major product. The stereochemistry of the product is determined by the planar nature of the carbocation, allowing the chloride ion to attack from either side.

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Key Concepts

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

Cis-Trans Isomerism

Cis-trans isomerism refers to the different spatial arrangements of atoms in a molecule, particularly in cyclic compounds. In the case of cis-2-methylcyclohexanol, the methyl group and the hydroxyl group are on the same side of the cyclohexane ring, influencing the reactivity and sterics during reactions. Understanding this concept is crucial for predicting how the molecule will interact with reagents like the Lucas reagent.

Lucas Reagent

The Lucas reagent, typically a mixture of zinc chloride and hydrochloric acid, is used to convert alcohols into alkyl halides. It works through the formation of a carbocation intermediate, which is more favorable for secondary and tertiary alcohols. Recognizing how the Lucas reagent functions helps in understanding the mechanism of the reaction and the stability of the resulting carbocation.

Carbocation Stability

Carbocation stability is a key concept in organic chemistry, as the stability of the carbocation intermediate significantly influences the reaction pathway. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects. In the reaction of cis-2-methylcyclohexanol with the Lucas reagent, the formation of a stable carbocation leads to the major product, 1-chloro-1-methylcyclohexane.

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Related Practice

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 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)

Textbook Question

Propose a mechanism for the reaction of

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

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.)

Textbook Question

Protonation converts the hydroxy group of an alcohol to a good leaving group. Suggest a mechanism for each reaction.

(a)

Textbook Question

What product would be formed if the four-membered ring alcohol in Problem 70 were heated with an equivalent amount of HBr rather than with a catalytic amount of H₂SO₄?

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