Lab #6 SN2 Reactions

Objectives of Experiment

• Perform an SN2 reaction

• Evaluate effects of:

  • Steric hindrance

  • Nucleophilicity of the amine

  • Nature of the leaving group

SN2 Reaction Overview

• Alkyl halides can be converted to various functional groups through nucleophilic substitution.

• Reaction is second-order (bimolecular) involving a single transition state.

Factors Affecting SN2 Reactions

• Favorable conditions:

  • Methyl > 1° > 2° alkyl halides (less steric hindrance)

  • 3° alkyl halides DO NOT undergo SN2 reactions.

  • Polar aprotic solvents enhance nucleophilicity (do not stabilize nucleophile well).

  • Strong nucleophiles are essential for reaction rate-determining step.

  • Good leaving groups must be present (e.g., weak bases, electron-withdrawing groups).

Experimental Procedure

Part A: Effect of Nucleophile

• Test various nucleophiles (triethyl amine, tripropyl amine, ethyldiisopropyl amine) with methyl iodide in solvent mixture.

• Record observations (precipitation time, color, texture).

Part B: Effect of Substrate and Leaving Group

• Use triethyl amine with iodoethane, 1-bromopropane, and 2-bromopropane in neat conditions.

• Record observations during reaction.

Part C: Unknown Amine Determination

• Combine unknown amine with iodomethane and solvent, allow to react then employ vacuum filtration.

• Measure melting points of resulting quaternary ammonium salts to identify unknown amine and determine % yield.