Substitution Solutions

The above substitution mechanism is bimolecular (SN₂) because there is a strong nucleophile given as well as an aprotic solvent. Remember: a strong nucleophile favors SN₂ and an aprotic solvent will also favor SN₂.

The above substitution mechanism is unimolecular (SN₁) because there is not a strong nucleophile present. Remember: a weak nucleophile favors SN₁ and because the electrophile leaves first, a carbocation is formed. Therefore, the nucleophile, CH₃CH₂CH₂OH can attack both the front and the back, resulting in a racemic mixture.