SN1 and SN2 reactions are the core template for alkyl-halide chemistry and a proving ground for mechanistic reasoning about rate, structure, and stereochemistry.
Differentiate SN1 and SN2 by rate law, substrate preference, stereochemical outcome, and solvent effects.
Predict when leaving-group quality and nucleophile strength will accelerate or redirect substitution.
Recognize conditions that allow carbocation rearrangement in SN1 chemistry.
Decide when substitution is likely to compete with elimination and how to bias the outcome.
Checkpoint Questions
Q: Why does sodium cyanide in DMSO often give strong SN2 reactivity?
A: Cyanide is a strong nucleophile and DMSO is polar aprotic, so the nucleophile is not heavily solvated and can attack efficiently.
Q: Why are allylic bromides often reactive in both SN1 and SN2 chemistry?
A: They can stabilize a carbocation by resonance and they are also less sterically blocked for backside attack.