Wize University Organic Chemistry Textbook > Nucleophilic Substitutions and Elimination Reactions
Solvent Effects in Substitution Reactions
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Solvent Effects in Substitution Reactions
Solvent can have a big effect on the SN1 and the SN2 reaction since both reactions proceed through either a transition state or intermediate (or both!)
The SN2 reaction
The SN2 reaction have high-energy transition states which carry partial charges. To stabilize this transition state, it is best to use polar solvents without protons (remember, there are strong nucleophiles present)! This is called a polar aprotic solvent. Examples include:
- acetone
- dimethylsulfoxide (DMSO)
- dimethylformamide (DMF)
- hexamethylphosphoramide (HMPA)
Examples reactions are shown below:
The SN1 reaction
The SN1 reaction have carbocation intermediates which carry formal positive charges. To stabilize this intermediate, it is best to use polar solvents with protons (because the nucleophiles are weak)! This is called a polar protic solvent. Examples include:
- water (H2O)
- alcohols (ROH, usually MeOH or EtOH)
- amines (usually NH3)
- carboxylic acids (RCOOH, usually acetic acid)
