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      Aldol Condensation reaction     

  Today i am talking  about Aldol Condensation reaction ,When I read first time Aldol i was think Aldol is name of a chemist like some other reactions in chemistry but it is not a name of Chemist, it is formed by two word ALD+OL where ALD means ALDEHYDE while OL means ALCOHOL😃 becouse the product of this reaction contain aldehyde or carbonyl group with alcohol group and this rxn was discovered by two chemist Alexander Borodin in 1869 and Charles-Adolphe Wurtz in 1872 ,if you want to know about these chemist more you can search easily on wikipedia.

                       
Content of Post➤
1.Definition   
2.Basic Tool
3.HOMO & LUMO Trick
4.Example taking Acetaldehyde Aldol condensation
5.Mechanism in Acidic & Basic mediam
6.Dehydration Steps
7.Restriction & Crossed-Aldol reaction       
8.Claisen-Schmidt Reaction
9.Aldol-condensation with Ketone


Now,I start ALDOL condensation  reaction ::


 "When Aldehyde or Ketone with alpha-H are present with acid or base then they give self-condensation reaction and give the beta-hydroxy carbonyl compound as a product"

#Basic tool



 as we all know that carbonyl carbon is electrophilic in nature and with neucleophile, it easily react but where is neucleophile??😮
       Lets start thinking about neucleophile.
In definition it is mention that acid or base is present .Now focus here ---when acid or base are present then The carbonyl compound with alpha-H converted into neucleoohile and then this neucleophile react with electroohilic carbonyl carbon and product formed easily.😃

In nucleophile, the carboanion is good nucleophile rather than the oxygen anion becouse the Highly occupied molecular energy(HOMO) of carbon is higher than the oxygen ,so its interaction with carbonyl carbon is better.
{To understand HOMO & LUMO ,read Molecular orbital Theory}

                               
Let us consider a simple example  of Acetaldehyde to explain Aldol Condensation MECHANISM .

Acetaldehyde with acid base in Aldol condensation give beta-hydroxy butanaldehyde as an Aldol product


 MECHANISM↠

Aldol Condensation reaction has different mechanism in acidic and basic mediam ,that i explain one by one.

                 
  1--IN BASIC MEDIAM➠
          Here the nucleophile is enolate ion .




                   
 2--IN ACIDIC MEDIAM➠
Here the nucleophile is enol which is bad nucleophile than  the enolate ion but in acidic mediam the carbonyl carbon become more electrophilic due to the presence of Acid becouse acid makes the carbonyl oxygen more electron needy ,so carbonyl [C=OH+ ]bond break fastly .
Here acetaldehyde become more electrophilic

  

 Both mechanism give same aldol But when aldol is heated more it easily release the water molecule and forms a conjugated carbonyl compound.

 *In presence of base it proceed via E1CB mechanism .
E1CB :conjugate base unimolecular elimination


*In acid it proceed via E1 mechanism.
E1:Unimolecular elimination without any strong base

* Restriction in aldol reaction is that if more than one alpha-H are present then mixture of products are formed,hence to remove this restriction only one type of alpha-H must present.
If two different type of aldehydes are used then reaction is called Crossed-Aldol reaction and mostly it give mixture of Aldol products.
it is also a example of cross-aldol rxn

*If Benzaldehyde is used as a electrophile here then the reaction is known as claisen-schmidt condensation.


Benzaldehyde as Electrophile & Acetone give enolate as nucleophile

  

 *Ketone also give Aldol rxn and product is known as Ketol but ketone give less afficient than Aldehyde due to Stearic hindrance and reaction product again converted into Reactant.





 NOTE::Aldol condensation is not ending here Picture abhi baki hai mere dosto.
This post is sufficient to class12 to B.sc. becouse some rxn like Mukaiyama aldol and Evans aldol reaction are also found but for these Stereochemistry knowledge is important..
if you wants stereochemical affect on Aldol reaction please comment then i will update it.
                               

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