Effect of Solvent Polarity on SNAr (Addition–Elimination)
- The key step forms a charged intermediate (Meisenheimer complex).
- Polar solvents stabilize this negative charge.
- So, higher polarity = faster reaction.
- Example: Reaction is faster in DMSO, DMF, or water than in nonpolar solvents.
Effect on Benzyne Mechanism
- Benzyne is a neutral intermediate (no charges).
- Solvent polarity has less effect on its rate.
- Reaction depends more on the strong base used.
In short:
- SNAr: polar solvents speed up the reaction.
- Benzyne: solvent polarity doesn’t matter much.