Textbook Question
Predict the major products of the following reactions. Include stereochemistry where applicable.
(c)
10. Addition Reactions
Hydroboration
5:51 minutesProblem 10c,d
Textbook Question
Predict the major products of the following reactions.
(c) 2-methylpent-2-ene + BH3⋅THF
(d) the product from part (c) + H2O2/OH−
Verified step by step guidance1
Step 1: Recognize that the reaction in part (c) involves hydroboration of 2-methylpent-2-ene with BH₃·THF. Hydroboration is an anti-Markovnikov addition of hydrogen (H) and boron (BH₂) across the double bond. The boron atom will attach to the less substituted carbon of the double bond, while the hydrogen will attach to the more substituted carbon.
Step 2: Draw the structure of 2-methylpent-2-ene and identify the double bond. Determine which carbon is less substituted (fewer alkyl groups attached) and which is more substituted. This will guide the placement of the BH₂ group and the H atom.
Step 3: After the hydroboration step, the product will be an organoborane intermediate where the BH₂ group is attached to the less substituted carbon of the double bond. Ensure the stereochemistry is considered, as hydroboration is a syn addition (both H and BH₂ add to the same face of the double bond).
Step 4: In part (d), the organoborane intermediate reacts with H₂O₂ (hydrogen peroxide) in the presence of OH⁻ (a base). This step is an oxidation reaction that replaces the BH₂ group with an OH group, forming an alcohol. The product will retain the anti-Markovnikov regiochemistry established in the hydroboration step.
Step 5: Draw the final product of part (d), ensuring the OH group is attached to the less substituted carbon of the original double bond. Confirm that the stereochemistry is consistent with the syn addition from the hydroboration step.
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Video duration:
5mKey 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) to form an organoborane intermediate, which is then oxidized in the second step by hydrogen peroxide (H2O2) in the presence of a base (OH−). This reaction is notable for its anti-Markovnikov addition, where the hydroxyl group attaches to the less substituted carbon of the alkene.
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General properties of hydroboration-oxidation.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the context of hydroboration-oxidation, the regioselectivity is influenced by the mechanism of the reaction, leading to the formation of the alcohol at the less substituted carbon atom of the alkene, which is a key feature of this reaction pathway.
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Stereochemistry
Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the case of the hydroboration-oxidation reaction, the stereochemistry of the product can be influenced by the formation of the organoborane intermediate, which can lead to the generation of chiral centers. Understanding stereochemistry is crucial for predicting the specific isomers formed in the final product.
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