7.2 SN1 Reactions
SN1 reactions – Substitution Nucleophilic Unimolecular
Unimolecular – Only one reactant molecule is involved in the slow step and the rate law is 1st order.
Rate = k[substrate]
-The substrate is often al alkyl halide (Cl, Br, and I are good leaving groups).
-The intermediate is a carbocation.
-Carbocation rearrangements are possible.
-Addition of AgNO3 can facilitate carbocation formation.
Predict the major substitution product for the following reaction.
Show the mechanism for how the product below was formed.
-SN1 reactions result in racemization at a chiral center (slight excess of the inverted product).
-All about carbocation stability
-Weak nucleophiles (or low concentrations of strong nucleophiles) are ok as it isn’t involved in the slow step.
-Water and alcohols are common nucleophiles in SN1 reactions.
Polar protic solvents are necessary to stabilize the carbocation (ion-diple forces).
-Water and alcohols are common solvents.
-Solvolysis – Many SN1 reactions involve the solvent as a reactant and are called solvolysis reactions.
Leaving Group Effects
-Generally the weaker the base the better the leaving group; the better the leaving group the faster the reaction.