Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions

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

Bruice 8th Edition

Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions

Problem 11a

Chapter 7, Problem 11a

What is the major product obtained from the acid-catalyzed hydration of each of the following alkenes?
a. CH₃CH₂CH₂CH=CH₂

Verified step by step guidance

Step 1: Understand the reaction mechanism. Acid-catalyzed hydration of alkenes involves the addition of water (H₂O) across the double bond in the presence of an acid catalyst, typically H₂SO₄ or H₃PO₄. The reaction proceeds via a Markovnikov addition, where the hydroxyl group (-OH) attaches to the more substituted carbon atom.

Step 2: Identify the structure of the alkene provided in the problem. Determine the position of the double bond and the substituents attached to the carbon atoms involved in the double bond.

Step 3: Protonation of the alkene. The acid catalyst donates a proton (H⁺), which adds to one of the carbon atoms in the double bond, forming a carbocation intermediate. The stability of the carbocation is crucial, as the reaction will favor the formation of the most stable carbocation (tertiary > secondary > primary).

Step 4: Nucleophilic attack by water. The water molecule acts as a nucleophile and attacks the carbocation, forming an oxonium ion (R-OH₂⁺). This step leads to the addition of the hydroxyl group (-OH) to the more substituted carbon atom.

Step 5: Deprotonation. The oxonium ion loses a proton (H⁺) to form the final alcohol product. The major product is determined by the Markovnikov rule, where the -OH group is added to the more substituted carbon atom of the original double bond.

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Key Concepts

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

Acid-Catalyzed Hydration

Acid-catalyzed hydration is a reaction where an alkene reacts with water in the presence of an acid catalyst, typically sulfuric acid. This process involves the formation of a carbocation intermediate, which is then attacked by water, leading to the formation of an alcohol. The regioselectivity of the reaction follows Markovnikov's rule, where the more substituted carbon of the alkene becomes bonded to the hydroxyl group.

Markovnikov's Rule

Markovnikov's rule states that in the addition of HX (where X is a halogen or hydroxyl group) to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This rule helps predict the major product of the reaction, as it favors the formation of the more stable carbocation, which is typically more substituted and thus more stable due to hyperconjugation and inductive effects.

Carbocation Stability

Carbocation stability is a key concept in organic chemistry that refers to the relative stability of positively charged carbon species. Carbocations are classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the positively charged carbon. Tertiary carbocations are the most stable due to greater hyperconjugation and inductive effects from surrounding alkyl groups, making them more favorable intermediates in reactions such as acid-catalyzed hydration.

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Related Practice

Textbook Question

Answer the following questions about the mechanism for the acid-catalyzed hydration of an alkene:

a. How many transition states are there?

b. How many intermediates are there?

c. Which step in the forward direction has the smallest rate constant?

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Textbook Question

What is the major product obtained from the acid-catalyzed hydration of each of the following alkenes?

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Textbook Question

What is the major product of each of the following reactions?

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Textbook Question

The pK_a of a protonated alcohol is about -2.5, and the pK_a of an alcohol is about 15. Therefore, as long as the pH of the solution is greater than _______ and less than _______, more than 50% of 2-propanol (the product of the reaction on p. 244) will be in its neutral, nonprotonated form.

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Textbook Question

What is the major product of each of the following reactions?

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Textbook Question

What alkene should be used to synthesize each of the following alkyl bromides?

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