Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds

Problem 86

Chapter 11, Problem 86

Propose a mechanism for the following reaction:

Verified step by step guidance

Step 1: Recognize the reaction type. This is an acid-catalyzed dehydration of an alcohol, where the hydroxyl group (-OH) is removed, and a double bond is formed in the product. The catalyst is sulfuric acid (H₂SO₄), and heat is applied to drive the reaction forward.

Step 2: Protonation of the alcohol group. The sulfuric acid donates a proton (H⁺) to the hydroxyl group (-OH) of the alcohol, converting it into a better leaving group, water (H₂O). The structure now contains a positively charged oxonium ion.

Step 3: Formation of the carbocation intermediate. The water molecule leaves, resulting in the formation of a carbocation at the carbon where the hydroxyl group was originally attached. This is the rate-determining step of the reaction.

Step 4: Rearrangement of the carbocation (if necessary). In this case, no rearrangement is needed because the carbocation is already on a secondary carbon, which is relatively stable.

Step 5: Elimination to form the alkene. A proton is removed from a neighboring carbon atom by a base (often HSO₄⁻ from the sulfuric acid), leading to the formation of a double bond between the carbons. This results in the final alkene product and regenerates the acid catalyst.

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Key Concepts

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

Reaction Mechanism

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, and the intermediates formed during the reaction. Understanding the mechanism is crucial for predicting the products and the conditions under which the reaction occurs.

Nucleophiles and Electrophiles

Nucleophiles are species that donate an electron pair to form a chemical bond, while electrophiles are electron-deficient species that accept an electron pair. Identifying these species in a reaction is essential for proposing a mechanism, as it helps to determine the flow of electrons and the formation of new bonds during the reaction.

Transition States and Intermediates

Transition states are high-energy states that occur during the transformation from reactants to products, representing the point of maximum energy along the reaction pathway. Intermediates are species that are formed and consumed during the reaction but are not present in the final products. Understanding these concepts is vital for accurately depicting the mechanism and predicting the reaction's rate and outcome.

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Intermediates vs. Transition States

Related Practice

Textbook Question

The following reaction takes place several times faster than the reaction of 2-chlorobutane with HO^-:

b. Explain why the OH group in the product is not bonded to the carbon that was bonded to the Cl group in the reactant.

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Textbook Question

The following reaction takes place several times faster than the reaction of 2-chlorobutane with HO^-:

a. Explain the enhanced reaction rate.

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Textbook Question

b. A small amount of a product containing a six-membered ring is also formed. Draw the structure of that product.

c. Why is so little six-membered ring product formed?

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Textbook Question

a. Propose a mechanism for the following reaction:

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Textbook Question

Triethylene glycol is one of the products obtained from the reaction of excess ethylene oxide and hydroxide ion. Propose a mechanism for its formation.

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Textbook Question

Which of the following reactions occurs more rapidly?

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