SN2 Reaction Conditions
SN2: Strong Nucleophile, Small substrate (1°), aprotic Solvent
Remember the conditions that favor SN2 over SN1: strong nucleophile, primary (small) substrate, and polar aprotic solvent. The opposite conditions favor SN1.
Breakdown
Strong
Strong nucleophile (CN-, I-, RS-)
Nucleophile
Attacks electrophilic carbon
Bimolecular
Rate depends on both reactants
Primary
Less steric hindrance for backside attack
Aprotic
Polar aprotic solvent (DMSO, DMF)
Inversion
Stereochemistry inverts!
Example
CH3CH2Br + CN- in DMSO -> SN2 (strong nucleophile + primary substrate + polar aprotic). (CH3)3CBr + H2O -> SN1 (weak nucleophile + tertiary + polar protic).
When to Use This
- ✓Predicting substitution mechanisms
- ✓Understanding stereochemical outcomes
- ✓Designing synthesis routes
- ✓Analyzing reaction conditions
FAQs
Common questions about this mnemonic
SN2 requires backside attack by the nucleophile. In tertiary substrates, three bulky groups block the backside, making SN2 sterically impossible. They can only react via SN1.
Polar protic solvents (water, alcohols) hydrogen-bond to nucleophiles, reducing their reactivity and favoring SN1. Polar aprotic solvents don't solvate nucleophiles, keeping them "naked" and reactive for SN2.