#This reaction involved two step mechanism.
#This reaction is characteristic reaction for carbonyl compounds.
#This reaction is not much often in the unsaturated olifiens.This is because of the pi-electron density in the double bonded compounds repel the nuclo-phyl.
#But those double bonded compounds containing good electron with drawing groups like -CN -CHO
can under go this type of reactions.
#Generally the base catalyzed nucliophylic addition reaction is more favorable than that of acid catalyzed, because acid decreases the nucliophyl conc.
#But there are some examples in which the nucliophylic addition facilitated by acid catalizetion.
For example,
1.Formation of acetals from aldehydes and alcohols.
2.Addition of RMgX on carbonyls facilitated by MgBr2.
#Addition of NaHSO3 on carbonyls need not a catalyst because , SO3 2- is a strong nucliophyl.
#Hence the attach of the nuclophyl is the slower and rate determining step.
#Addition of HCl on carbonyl is not possible because Cl- is good leaving group, so again elimination of HCl takes place and leads to carbonyl compound.
STEREO CHEMISTRY OF THE REACTION:
#Since the carbonyls SP2 hybridized they are sqare triangular. i.e planar. So 50% chance is there to attack the nuclophil on the carbonyl carbon from each side. So resimarizetion of product is result.
#so as shown in the figureresimic mixture will be formed
due to equal probable attack from
the both sides of carbonyl carbon.
LESS CHANCE OF 50-50 ENATIOMERS (NO PERFECT RECIMERIZETION)
#If there is bulky group present on the alpha
carbon of the carbonyl carbon then the attach
of nucliophy is from the liter group, side which
is having lower energy path which is sterecally
and energetically favorabl.
#So unequal diastereomers will be formed and
hence not complete recimerizetion occur.
ENERGY PROFILE DIAGRAM:
In case of base catalyzed mechanism:
In case of acid catalyzed mechanism:
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