SN1/SN2 Reactions

SN2 Reactions

• Occurs in one step

  • The leaving group leaves and is replaced by the nucleophile in the same step

• Main Factor: Steric Hindrance

  • Whether or not the electrophile is surrounded by many R groups

• Methyl alkyl halides are the best electrophiles for this reaction, followed by primary, then secondary alkyl halides

  • Tertiary alkyl halides will not react at all in an SN2 reaction, as they are too hindered

• Inversion occurs

  • Chiral centers invert configuration

SN1 Reactions

• Occurs in two steps

  • The leaving group leaves first, creating a carbocation where the leaving group left. The nucleophile then attacks this carbocation.

• Main Factor: Carbocation stability

  • How stable the carbocation is following its formation

• Tertiary alkyl halides are the best electrophiles for this reaction, followed by secondary alkyl halides

  • Primary and methyl alkyl halides will not undergo an SN1 mechanism, as their carbocations are unstable

• Both inversion and retention occurs

  • Chiral groups may or may not invert

  • Combination of both stereoisomers leads to a racemic mixture

• Carbocation rearrangements can occur

  • Done to lead to a more stable carbocation

  • Hydride shifts

    • A hydrogen moves to the position of the carbocation; seen when a secondary carbocation is next to a tertiary carbon

  • Methyl shifts

    • A carbon moves to the position of the carbocation; seen when a secondary carbocation is next to a quaternary carbon