Halides in Substitution Reactions
- Halides are compounds with a halogen (F, Cl, Br, I) attached to carbon.
- Halogens are good leaving groups, so they can be replaced by nucleophiles.
1. SN1 Reaction (Unimolecular)
- Happens mostly with tertiary or some secondary halides.
- Steps:
- Halogen leaves → forms a carbocation.
- Nucleophile attacks the carbocation → new product.
- Example: (CH₃)₃C–Br + H₂O → (CH₃)₃C–OH + HBr
2. SN2 Reaction (Bimolecular)
- Happens mostly with methyl or primary halides.
- Steps:
- Nucleophile attacks the carbon opposite the halogen (backside attack) → halogen leaves.
- Example: CH₃CH₂–Br + OH⁻ → CH₃CH₂–OH + Br⁻
Simple takeaway:
- Halides react because halogens leave easily, allowing nucleophiles to replace them.
- SN1 → tertiary/secondary, forms carbocation
- SN2 → primary/methyl, direct attack from nucleophile