further chem
look at the solvent
does the solvent stabilise the leaving group?
- yes means sn1 (polar protic)
- no means sn2 (polar non-protic)
polar aprotic solvents
- allows SN2
- leaves nucleophile unsolvated
- worse at stabilising carbocations and leaving groups
- because dipole is buried in solvent molecule vs protic solvents
- like delta positive of acetone is buried, hard to stabilise negative leaving groups
Why Protic Solvents Are Better for Carbocations (SN1)
- Hydrogen Bonding: Polar protic solvents (like water, alcohols) have H atoms bonded to O or N, allowing strong hydrogen bonds, which effectively stabilize the positive charge of a carbocation and the negative charge of the leaving group (halide).
- Dielectric Effect: Their high dielectric constant helps disperse charge, further lowering the energy of charged intermediates
protic solvents:
- stabilises carbocations