1. Lecture 7

2. Rearrangement Involving Carbocations Qn: Why is rearrangement quite common to carbocations, and not in case of radicals or anions? Formation of TS involves combination of bonding orbital (C-R)with the vacant orbital on the carbocation, singly occupied orbital in case of radical and doubly occupied orbital in case of carbanion.This overlap generates one bonding and one antibonding scenario. In case of cation, both the electrons occupy the bonding orbital……hence rearrangement is facile

3. Electron Deficient Carbon Carbene Reactions of Carbocations: 1)Combination with a nucleophile 2)Elimination of a proton 3)Addition to an unsaturated linkage 4)rearrangement

4. Qn: Why does the methyl migrate to a tertiary cation? Ans: To achieve greater stabilization by delocalization of charge through electron pair of oxygen atom.

5. For differently substituted pinacols How to decide which will be major? 1)First decide which carbocation is more stable 2)Then consider the relative migratory aptitude of the groups that will undergo 1,2-shift.

6. Migratory aptitude aryl>alkyl usually H>alkyl Aryl has greater migratory aptitude because it assists in the departure of leaving group (anchimeric assistance) Via bridged carbocation Electron donating groups at the ortho or para position will enhance the migratory aptitude while electron withdrawing groups will lower the aptitude for migration.

7. In case of hydride vs alkyl migration Hydride generally migrates because of the generation of a more stable carbocation Other ways of carrying out pinacol-pinacolone type rearrangements

8. Stereochemistry of migration: The migrating group retains configuration. That means migrating group is never totally detached This is also proved by cross over experimentsHome Assignment

9. LECTURE 8

10. Qn: Write down the Fisher projection formula of the major product Problems on Pinacol-pinacolone rearrangement

12. Migration to electron deficient Nitrogen Hofman, Curtius, Lossen, Schmidt

13. Problem

14. Beckman Rearrangement Anti group always migrates…no question of migratory aptitude! Mechanism

15. Rearrangement Involving Carbanions Favorskii Rearrangent Migration to electron Deficient Oxygen Bayer Villiger Oxidation

16. Earlier mechanism However Application to acyclic systems