Ch.8 - Reactions of Alkenes

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch.8 - Reactions of Alkenes

Problem 22c

Chapter 8, Problem 22c

Show how you would accomplish the following synthetic conversions.
c. 1-methylcyclopentanol → 2-chloro-1-methylcyclopentanol
Problem-Solving Hint: The opening of a halonium ion is driven by its electrophilic nature. The weak nucleophile attacks the carbon bearing more positive charge.

Verified step by step guidance

Step 1: Begin by understanding the target transformation. The goal is to convert 1-methylcyclopentanol into 2-chloro-1-methylcyclopentanol. This involves introducing a chlorine atom at the 2-position while retaining the hydroxyl group at the 1-position.

Step 2: Recognize that the reaction likely involves the formation of a halonium ion intermediate. To achieve this, treat the starting alcohol (1-methylcyclopentanol) with a halogen source, such as Cl₂, in the presence of a nucleophilic solvent like water. This will facilitate the formation of a halonium ion.

Step 3: The halonium ion intermediate forms when the double bond (if present) or the alcohol reacts with the halogen. The halonium ion is electrophilic, meaning it has a partial positive charge on the carbons involved in the ring structure. The nucleophile (water or hydroxyl group) will attack the more positively charged carbon in the halonium ion.

Step 4: After the nucleophilic attack, the halonium ion opens up, resulting in the addition of a chlorine atom to the 2-position and retention of the hydroxyl group at the 1-position. This regioselectivity is driven by the stability of the carbocation formed during the process.

Step 5: Finally, isolate and purify the product, 2-chloro-1-methylcyclopentanol, using standard organic chemistry techniques such as distillation or chromatography to ensure the desired compound is obtained.

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Key Concepts

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

Halonium Ion Mechanism

A halonium ion is a cyclic intermediate formed during the electrophilic addition of halogens to alkenes. This species is characterized by a three-membered ring structure where a halogen atom carries a positive charge. The electrophilic nature of the halonium ion makes it susceptible to nucleophilic attack, typically at the more substituted carbon, leading to the formation of products like 2-chloro-1-methylcyclopentanol.

Nucleophilic Attack

Nucleophilic attack refers to the process where a nucleophile, which is an electron-rich species, donates a pair of electrons to an electrophile, forming a new bond. In the context of the conversion from 1-methylcyclopentanol to 2-chloro-1-methylcyclopentanol, the weak nucleophile attacks the carbon of the halonium ion that bears a greater positive charge, facilitating the substitution reaction.

Electrophilicity and Reactivity

Electrophilicity is a measure of how readily a species can accept electrons, making it a key factor in chemical reactivity. In this synthetic conversion, the halonium ion's strong electrophilic character drives the reaction, as it attracts nucleophiles. Understanding the relative electrophilicity of different species helps predict the outcome of reactions, such as the formation of 2-chloro-1-methylcyclopentanol from 1-methylcyclopentanol.

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Related Practice

Textbook Question

Show how you would accomplish the following synthetic conversions.

a. 3-methylpent-2-ene → 2-chloro-3-methylpentan-3-ol

Problem-Solving Hint: The opening of a halonium ion is driven by its electrophilic nature. The weak nucleophile attacks the carbon bearing more positive charge.

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Textbook Question

Give the expected major product for each reaction, including stereochemistry where applicable.

(a) but-1-ene + H₂/Pt

(b) cis-but-2-ene + H₂/Ni

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Textbook Question

Predict the major product(s) for each reaction. Include stereochemistry where appropriate.

e. 1-methylcyclopentene + Br₂ in saturated aqueous NaCl

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Textbook Question

One of the principal components of lemongrass oil is limonene, C₁₀H₁₆. When limonene is treated with excess hydrogen and a platinum catalyst, the product is an alkane of formula C₁₀H₂₀. What can you conclude about the structure of limonene?

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Textbook Question

Show how you would accomplish the following synthetic conversions.

b. chlorocyclohexane → trans-2-chlorocyclohexanol

Problem-Solving Hint: The opening of a halonium ion is driven by its electrophilic nature. The weak nucleophile attacks the carbon bearing more positive charge.

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Textbook Question

Give the expected major product for each reaction, including stereochemistry where applicable.

(c)

(d)

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Show how you would accomplish the following synthetic conversions.c. 1-methylcyclopentanol → 2-chloro-1-methylcyclopentanolProblem-Solving Hint: The opening of a halonium ion is driven by its electrophilic nature. The weak nucleophile attacks the carbon bearing more positive charge.

Verified video answer for a similar problem:

Key Concepts

Halonium Ion Mechanism

Nucleophilic Attack

Electrophilicity and Reactivity

Show how you would accomplish the following synthetic conversions.
c. 1-methylcyclopentanol → 2-chloro-1-methylcyclopentanol
Problem-Solving Hint: The opening of a halonium ion is driven by its electrophilic nature. The weak nucleophile attacks the carbon bearing more positive charge.