SN2, E2, SN1, and E1 Reactions

SN2 Reaction

Bimolecular nucleophilic substitution that requires strong nucleophiles and is sensitive to steric hindrance.

Substrate for SN2

Primary and some secondary alkyl halides.

Nucleophile for SN2

Strong nucleophiles like CN-, OH-, or RS-.

Solvent for SN2

Polar aprotic solvents such as DMF, DMSO, and acetone.

Stereochemistry of SN2

Inversion of configuration.

Kinetics of SN2

Second-order kinetics; rate depends on both substrate and nucleophile.

Preferred temperature for SN2

Generally favored at lower temperatures.

E2 Reaction

Bimolecular elimination that requires strong bases and specific stereochemistry.

Substrate for E2

Primary, secondary, or tertiary alkyl halides.

Base for E2

Strong bases such as NaOEt or KOH.

Stereochemistry of E2

Requires an anti-periplanar arrangement.

Kinetics of E2

Second-order kinetics; rate depends on both substrate and base.

Products of E2

Can form Zaitsev (major) or Hofmann (minor) products.

Preferred temperature for E2

Often requires heating.

SN1 Reaction

Unimolecular nucleophilic substitution characterized by weak nucleophiles and carbocation stability.

Substrate for SN1

Tertiary and some secondary alkyl halides.

Nucleophile for SN1

Weak nucleophiles such as H2O or alcohols.

Solvent for SN1

Polar protic solvents like H2O or alcohols.

Stereochemistry of SN1

Leads to racemization (loss of stereochemistry).

Kinetics of SN1

First-order kinetics; rate depends only on substrate.

Carbocation stability in SN1

Important factor influencing reaction outcome.

E1 Reaction

Unimolecular elimination involving weak bases and polar protic solvents.

Substrate for E1

Tertiary and some secondary alkyl halides.

Base for E1

Weak bases or solvent acting as base.

Solvent for E1

Polar protic solvents such as H2O or alcohols.

Kinetics of E1

First-order kinetics; rate depends only on substrate.

Products of E1

Generally favors Zaitsev product (more substituted alkene).

Preferred temperature for E1

Often requires heating.

Common factors for all reactions

Better leaving groups, resonance stabilization, higher concentrations, and temperature effects favor elimination.