The mechanism of electrophilic addition explains how alkenes and alkynes (which have electron-rich multiple bonds) react with electrophiles. Here’s the step-by-step process in simple words:
1. Attack of the electrophile
- The double bond in an alkene has a high density of electrons.
- An electrophile (something electron-loving, like H⁺ from HBr, Br₂, or other reagents) gets attracted to this electron-rich bond.
- One carbon of the double bond bonds with the electrophile.
2. Formation of carbocation (or similar intermediate)
- When the double bond breaks, one carbon becomes positively charged.
- This creates a carbocation, which is unstable and short-lived.
- The stability of this carbocation is very important: more stable carbocations form more easily.
3. Attack of the nucleophile
- A nucleophile (something with extra electrons, like Br⁻, Cl⁻, OH⁻, etc.) then attacks the carbocation.
- This forms a new bond and completes the addition.
4. Product formation
- The final product is a saturated compound (for alkenes, it becomes an alkane derivative).
- The position of atoms added often follows Markovnikov’s rule, where the electrophile attaches to the carbon with more hydrogens, giving the more stable carbocation.
In short:
Electrophilic addition happens in three stages —
- Electrophile attacks the double bond.
- Carbocation forms.
- Nucleophile attaches to the carbocation, giving the final product.