pinacole pinacolone rearrangement

1. S.P.C. GOVT. COLLEGE AJMER
DEPARTMENT OF CHEMISTRY
2022-2023
SUBMITTED BY- VISHAL ARORA
M.SC. CHEMISTRY (SEMESTER 4th
)
TOPIC
Pinacol Pinacolone rearrangement

2. Content:-
About Reaction
Mechanism
Migratory aptitude
Stereochemistry
Applications

3. SUBSTRATE:- Pinacol(1,2 -glycols)
REACTION CONDITIONS:- Mineral acids and zinc
chloride, acid chloride or other electrophilic reagents
Product:- ketones or aldehyde
 In this rearrangement carbocation is form as intermediate.
 It is a anionic rearrangement or nucleophilic group moves from a
carbon atom to an electron defficient carbon which has only six
electrons in its valence shell.
 Image by https://slideplayer-com.cdn.ampproject.org

4. Mechanism:- case 1:- symmetrical
molecule

5. Images by https://slideplayer-com.cdn.ampproject.org

6. Case 2:- protonation occur at which OH
(1 OR 2)
 When an unsymmetrical diol rearranges there is choice as to
which hydroxy group will be removed.
 The hydroxy group lost should be the one that leaves behind the more
stable carbocation.


7. CASE 3:- WHICH GROUP WILL MIGRATE ?
(MIGRATORY APTITUDE)
 Migratory ability of a group is mainly related to its capacity to render
ANCHIMERIC ASSISTANCE to the departure of the nucleofuge.
 ANCHIMERIC ASSISTANCE:- Neighbouring group participation in the
increasing the rate of departure of leaving group.
 In this rearrangement the order prefer for migrating aptitude is
ARYL>ALKYL(3˚>2˚>1˚)>HYDROGEN
 In this series the position of hydrogen is unpredictable.

9. WHAT SHOULD BE THE STEREOCHEMISTRY
OF MIGRATING GROUP AND LEAVING GROUP
o In rigid cyclic there must be anti periplanar relationship
between migrating group and leaving group.
o The relation between H and N2
+ are anti periplanar.

10. APPLICATION:-
⚫ The reaction provides methods for the preparation of many
carbonyl compounds which are otherwise difficult to prepare.
⚫ Benzopinacol for example rearranges to benzopinacolone
when heated in acetic acid in presence of iodine as catalyst.
 ssImage by Claydon organic chemistry

11. ⚫ The pinacol pinacolone rearrangement is a very useful
general method for synthesis of spiroketones.
⚫ Image by clayden organic chemistry

12. Reference:-
AUTHOR NAME BOOK NAME EDITION
JERRY MARCH ADVANCED ORGANIC FOURTH
CHEMISTRY
REACTIONS,MECHANISMS
AND STRUCTURE
V.K. AHLUWALIA
R.K. PARASHAR ORGANIC REACTION
MECHANISM FOURTH
MORRISON & BOYD Organic chemistry SIXTH

13. Thank you