Textbook Question
Show how you would synthesize the following alcohol from appropriate alkene.
(b)
10. Addition Reactions
Hydroboration
4:27 minutesProblem 95b
Textbook Question
Draw the products of the following reactions, including their configurations:
Verified step by step guidance1
Step 1: Analyze the reaction labeled 'A'. The starting material is a cyclohexene derivative with a methyl group attached to the double bond. The reaction involves Br2 in CCl4, which is a halogenation reaction. This reaction adds bromine across the double bond in an anti-addition manner, resulting in a vicinal dibromide product.
Step 2: For reaction 'A', determine the stereochemistry of the product. Since bromine adds anti to the double bond, the two bromine atoms will be added to opposite faces of the cyclohexane ring. This results in a trans configuration of the bromine atoms.
Step 3: Analyze the reaction labeled 'B'. The starting material is the same cyclohexene derivative. The reaction involves hydroboration-oxidation, which is a two-step process. In the first step, BH3/THF adds across the double bond in a syn-addition manner, forming an organoborane intermediate.
Step 4: In the second step of reaction 'B', the organoborane intermediate is oxidized using H2O2 and HO-. This converts the boron group into a hydroxyl group (-OH). The hydroxyl group is added to the less substituted carbon of the double bond, following anti-Markovnikov regioselectivity.
Step 5: For reaction 'B', determine the stereochemistry of the product. Since hydroboration occurs via syn-addition, the hydroxyl group and the hydrogen added during the first step will be on the same face of the cyclohexane ring. This results in a specific stereochemical configuration for the product.
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4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydroboration-Oxidation
Hydroboration-oxidation is a two-step reaction process used to convert alkenes into alcohols. In the first step, an alkene reacts with borane (BH3) in a tetrahydrofuran (THF) solvent, resulting in the formation of an organoborane intermediate. The second step involves the oxidation of this intermediate using hydrogen peroxide (H2O2) and a hydroxide ion (HO-), yielding an alcohol with anti-Markovnikov selectivity.
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General properties of hydroboration-oxidation.
Anti-Markovnikov Addition
Anti-Markovnikov addition refers to the regioselectivity observed in certain reactions where the less substituted carbon of an alkene receives the electrophile. In the case of hydroboration, the boron atom attaches to the less substituted carbon, leading to the formation of an alcohol at that position after oxidation. This contrasts with Markovnikov's rule, where the more substituted carbon would typically receive the electrophile.
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Stereochemistry of Reactions
Stereochemistry involves the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In reactions like hydroboration-oxidation, the stereochemical outcome can be significant, as the addition of reagents can lead to different configurations (cis or trans) of the product. Understanding stereochemistry is crucial for predicting the configuration of the final products in organic reactions.
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