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.
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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.
8.
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