Textbook Question
What stereoisomers are obtained from each of the following reactions?
b.
10. Addition Reactions
Acid-Catalyzed Hydration
6:58 minutesProblem 6b,c
Textbook Question
Predict the products of the following hydration reactions.
b. 2-phenylpropene + dilute acid
c. 1-phenylcyclohexene + dilute acid
Verified step by step guidance1
Step 1: Understand the reaction type. Hydration reactions involve the addition of water (H₂O) across a double bond in the presence of an acid catalyst, typically dilute H₂SO₄ or H₃O⁺. This reaction follows Markovnikov's rule, where the hydrogen atom from water adds to the carbon with more hydrogens, and the hydroxyl group (-OH) adds to the carbon with fewer hydrogens.
Step 2: Analyze the structure of 2-phenylpropene. This molecule contains a double bond between the second and third carbons in the propene chain, with a phenyl group attached to the second carbon. Apply Markovnikov's rule to predict that the -OH group will add to the more substituted carbon (the second carbon), and the hydrogen will add to the less substituted carbon (the third carbon).
Step 3: Draw the product for 2-phenylpropene. After hydration, the double bond is broken, and the molecule forms 2-phenyl-2-propanol. The hydroxyl group (-OH) is attached to the second carbon, and the third carbon gains a hydrogen atom.
Step 4: Analyze the structure of 1-phenylcyclohexene. This molecule contains a double bond in the cyclohexene ring between the first and second carbons, with a phenyl group attached to the first carbon. Apply Markovnikov's rule to predict that the -OH group will add to the more substituted carbon (the second carbon), and the hydrogen will add to the less substituted carbon (the first carbon).
Step 5: Draw the product for 1-phenylcyclohexene. After hydration, the double bond is broken, and the molecule forms 1-phenylcyclohexanol. The hydroxyl group (-OH) is attached to the second carbon in the cyclohexane ring, and the first carbon gains a hydrogen atom.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydration Reactions
Hydration reactions involve the addition of water (H2O) to an alkene, resulting in the formation of alcohols. In the presence of an acid catalyst, the double bond of the alkene is protonated, leading to the formation of a more stable carbocation intermediate. This intermediate then reacts with water to yield the final alcohol product. Understanding the mechanism of hydration is crucial for predicting the products of the given reactions.
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Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX (where X is a halogen or OH) to an asymmetric alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the regioselectivity of the product formed during hydration reactions, guiding the placement of the hydroxyl group in the final alcohol product.
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Carbocation Stability
Carbocation stability is a key factor in determining the outcome of reactions involving alkenes. Carbocations are positively charged intermediates that can vary in stability based on their structure; tertiary carbocations are more stable than secondary, which are more stable than primary. The stability of the carbocation formed during the hydration of alkenes influences the product distribution, as more stable carbocations are favored in the reaction pathway.
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