Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook

Mullins 1st Edition

Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes

Problem 66c

Chapter 11, Problem 66c

Give a mechanism for the following substitution and elimination reactions.
(c)

Verified step by step guidance

Step 1: Analyze the reactant structure. The molecule contains a hydroxyl group (-OH) and a tertiary alkyl chloride (-Cl) group. The reaction occurs in the presence of water (H₂O), which can act as a nucleophile or solvent.

Step 2: Recognize the reaction type. The presence of a tertiary alkyl chloride suggests that the reaction may proceed via an SN1 (substitution) or E1 (elimination) mechanism due to the stability of the tertiary carbocation formed after the departure of the chloride ion.

Step 3: Initiate the mechanism. The chloride ion (Cl⁻) leaves, forming a tertiary carbocation. This step is the rate-determining step and is facilitated by the polar protic solvent (H₂O), which stabilizes the carbocation.

Step 4: Substitution pathway. Water (H₂O) acts as a nucleophile and attacks the carbocation, forming an oxonium ion. Deprotonation of the oxonium ion by another water molecule leads to the formation of the substitution product.

Step 5: Elimination pathway. A proton from a β-carbon adjacent to the carbocation is removed by water, leading to the formation of a double bond. The resulting intermediate undergoes intramolecular cyclization to form the cyclic ether product.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Was this helpful?

Key Concepts

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

Nucleophilic Substitution Mechanisms

Nucleophilic substitution reactions involve the replacement of a leaving group by a nucleophile. The two primary mechanisms are SN1 and SN2. SN1 is a two-step process where the leaving group departs first, forming a carbocation, followed by nucleophilic attack. In contrast, SN2 is a one-step mechanism where the nucleophile attacks the substrate simultaneously as the leaving group departs, leading to an inversion of configuration.

Elimination Reactions

Elimination reactions involve the removal of a small molecule, typically water or hydrogen halide, from a larger molecule, resulting in the formation of a double bond. The two main types are E1 and E2. E1 is a two-step process similar to SN1, where a carbocation intermediate is formed before the elimination occurs. E2 is a concerted mechanism where the base abstracts a proton while the leaving group departs, often requiring strong bases and specific stereochemistry.

Regioselectivity and Stereoselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others, while stereoselectivity indicates the preference for one stereoisomer over another. In substitution and elimination reactions, these concepts are crucial for predicting the major products. Factors influencing regioselectivity include the stability of intermediates and steric hindrance, while stereoselectivity is often influenced by the mechanism (SN1 vs. SN2) and the nature of the reactants.

Recommended video:

Guided course

05:09

Heck Reaction

Related Practice

Textbook Question

Which of the following substitution reactions would you expect to occur more quickly? Explain your answer.

views

Textbook Question

When trans-4-bromocyclohexanol is treated with base, an intramolecular substitution reaction occurs to give a cyclic ether. This product does not form when cis-4-bromocyclohexanol is reacted under the same conditions. Explain these observations.

views

Textbook Question

Give a mechanism for the following substitution and elimination reactions.

(b)

views

Textbook Question

The following chlorocyclohexane undergoes neither Sₙ2 nor E2 under the conditions shown. Why?

views

Textbook Question

Give a mechanism for the following substitution and elimination reactions.

(a)

views