Assignment No 2 Title: Enolization Course code: CHEM-522 Submitted

              Assignment  No  2

  

 

 

       Title:

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                             Enolization

       Course  code:

                                    CHEM-522

 
     Submitted  By:

                             Zunaira Arshad

                            17101707-043

                            M.Phil 
B

       Submitted To:

                       Dr.Sajjad 
Sumerra 

       

 

            

                  Enolisation

Definition:

              A   process 
in which an aldehyde or ketone is converted  into its 
corresponding

Enole  is called  enolization or keto-enol  tautomerism.1

           Chemistry  of Carbonyl compound

v
Nature of carbonyl
compound and Reactivity;

Carbonyl
compound is very versatile and it contains partial positive charge on carbon
and partial negative charge on oxygen.

                   

Important
points in its chemistry are;

1.Carbon
and Oxygen are sp2 hybridized

2.Carbon
form single bond with other R  groups

3.Two
lone pairs are present on oxygen atom

The
geometery or framework of carbonyl 
compound is  Trigonal Planner.

     
While the reactivity of carbonyl
compound  is  due to the presence of  acidic ?-hydrogen.

                          

Since
in alkanes hydrogen is bonded to carbon by sp3 hybridization but the
electronegativity difference between carbon and hydrogen is  so small due to which the attatched hydrogen
is less acidic.While in the case of aldehyde or ketone due to the presence of
carbonyl group to the ?-carbon the ?-hydrogen becomes  more acidic.But still this ?-hydrogen is less
acidic then hydrogen of H2O.

    CH3CH3            

                        

                    

Actually
two main factors responsible for acidity of carbonyl compounds are;

1. 
Inductive effect of carbonyl
compound  increases the pocitive character
of ?-hydrogen

2. 
Resonance stabilization
of conjugate base

Since
above values shows that aldehyde and ketones are more acidic  then sp3 hybridized Carbon  as alkanes.Because

After
the removal of ?-hydrogen the conjugate
base formed is more stable in carbonyl containing compounds due to resonance
than sp3 hybridized carbon.

                        

                

Similarly
aldehyde and ketone are more acidic than ethers for the same reason which is
described above and ethers are less acidic because after removal of ?-hydrogen
in ethers the non-bonding electrons of OR and O compete for resonance.

               

When ?-hydrogen
is present between two carbonyl compounds then pka of ?-diketoester  is more then pka of ?-diketones i.e ?-diketoester
is less acidic then ?-dietones.