Answer
🧪 Reagent Matching for Alkene Transformations
Objective
To identify the correct reagents needed to accomplish specific alkene transformations based on their mechanisms and regioselectivity.
Overview
Alkenes undergo several types of addition reactions which can differ based on:
- Regioselectivity: Markovnikov vs. anti-Markovnikov addition
- Stereochemistry: Syn- vs. anti-addition
- Reaction Intermediates: Carbocations, halonium ions, or cyclic intermediates
Reactions and Their Reagents
1. Oxymercuration-Demercuration
- Purpose: Markovnikov addition of OH
- Reagents:
Hg(OAc)â‚‚, Hâ‚‚O / NaBHâ‚„ - Intermediate: Mercurinium ion (no rearrangement)
- Result: OH on more substituted carbon, anti-addition
2. Hydroboration-Oxidation
- Purpose: Anti-Markovnikov addition of OH
- Reagents:
BH₃·THF / H₂O₂, NaOH - Intermediate: Borane complex
- Result: OH on less substituted carbon, syn-addition
3. Acid-Catalyzed Hydration
- Purpose: Markovnikov addition of OH
- Reagents:
Hâ‚‚O / Hâ‚‚SOâ‚„ - Intermediate: Carbocation (rearrangement possible)
- Result: OH on more substituted carbon
4. Halohydrin Formation
- Purpose: Addition of OH and halogen (e.g., Br)
- Reagents:
Brâ‚‚ / Hâ‚‚O - Intermediate: Bromonium ion
- Result: OH on more substituted carbon, anti-addition
Summary Table
| Transformation | Regioselectivity | Stereochemistry | Reagents |
|---|---|---|---|
| Oxymercuration-Demercuration | Markovnikov | Anti | Hg(OAc)â‚‚, Hâ‚‚O / NaBHâ‚„ |
| Hydroboration-Oxidation | Anti-Markovnikov | Syn | BH₃·THF / H₂O₂, NaOH |
| Acid-Catalyzed Hydration | Markovnikov | Not stereoselective | Hâ‚‚O / Hâ‚‚SOâ‚„ |
| Halohydrin Formation | Markovnikov (OH) | Anti | Brâ‚‚ / Hâ‚‚O |
Conclusion
Correct identification of reagents depends on understanding both the regiochemical outcome (Markovnikov vs. anti-Markovnikov) and the reaction mechanism. This knowledge is fundamental for designing efficient and selective alkene transformations in organic synthesis.