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SN1 Mechanism: Solvolysis

CH 6-6 SN1 Reaction – Part III. SN1 Mechanism: Solvolysis. Lets think about what the mechanism might look like:. First, can we confirm that this substitution reaction follows an SN1 mechanism and not SN2?. How many steps are needed?. What is the RLS?. What does the energy diagram look like?.

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SN1 Mechanism: Solvolysis

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  1. CH 6-6 SN1 Reaction – Part III SN1 Mechanism: Solvolysis • Lets think about what the mechanism might look like: • First, can we confirm that this substitution reaction follows an SN1 mechanism and not SN2? • How many steps are needed? • What is the RLS? • What does the energy diagram look like? • What does the TS structure look like?

  2. SN1 Mechanism: Solvolysis

  3. 2o Substrates: SN1 or SN2? • Is the mechanism SN1 or SN2? • An SN1 mechanism is favored by weak nucleophiles (H2O, ROH) and polar, protic solvents (i.e., the solvent is the nucleophile - Solvolysis). • An SN2 mechanism is favored by good nucleophiles, and polar, aprotic solvents. What are a few “good” nucleophiles?

  4. Keys to Identifying Substitution Reactions (1) Identify the electrophilic carbon (d+) in the substrate: methyl or 1o = SN2…….…….… 3o = SN1…….………. 2o = either (see Nucleophile) (2) Identify the nucleophile (weak or strong base?)H2O or ROH = usually SN1…..”good” Nuc/strong base or Cl-, Br-, I-, -CN, NH3 = usually SN2 (3) Identify the leaving group - must form a weak base! (halide ion) (4) What type of solvent is being used? polar protic = usually SN1………….……polar aprotic = usually SN2 (5) What is the Substitution mechanism? (SN2 or SN1) (6) Draw the products with the proper structure and stereochemistry: SN1 = racemic mixture & possible rearrangement………..SN2 = inversion of configuration

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