7 Important Concepts Important Concepts 1.Unimolecular Substitution in Polar Modia- 不Rascemtatena9eaausponnmoeoaa 2 ent of the leaving ophile changes the product,but not the 7。 Carbocation Stabilization by 5llnatioar5ay9cedc.e8yhegereadsubsrate 77 7 Important Concepts 1. Unimolecular Substitution in Polar Media – • Secondary haloalkanes: slow • Tertiary haloalkanes: fast • When the solvent is the nucleophile, the process is called solvolysis. 2. Rate-Determining Step in Unimolecular Substitution – • Dissociation of the C-X bond to form a carbocation intermediate • Added strong nucleophile changes the product, but not the reaction rate 3. Carbocation Stabilization by Hyperconjugation– • Tertiary > Secondary • Primary and methyl unstable 7 Important Concepts 4. Racemization – Often occurs upon unimolecular substitution at a chiral carbon. 5. Unimolecular Elimination – Alkene formation accompanies substitution in secondary and tertiary system. 6. Bimolecular Elimination – May result from high concentrations of strong base. The elimination involves the anti conformational arrangement of the leaving group and the extracted hydrogen. 7. Substitution Favored – By unhindered substrates and small, less basic nucleophiles 8. Elimination Favored – By hindered substrates and bulky, more basic nucleophiles