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?

SN1 Mechanism: Solvolysis

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?

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