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Manasi (3976)

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calculation of no of optical isomers.....
 
Type 1 : when molecule is not divisible into two equal halves and contains 'n'
asymmaetric carbon atoms, then
no of optically active isomers (a) = 2^n
no of meso forms, (m) = 0
no of racemice mixture (r) = a/2
Note : racemice forms will never be included in total no of optical isomers
Total no of optical isomers =a + m
e.g no of optical active isomers of glucose
      = total no of isomers of glucose
      = 2^ 4 =16
 
 
Type 2: When molecule is divisble in two equal halves,
case (i) if n is even,
            then a= 2^(n-1)
                    r= a/2
                    m= 2^{(n/2)-1}
total no of isomers =a +m
 
Case (ii) if n is odd, a= [{2 ^(n-1)} - {2 ^ (n-1)/2}]
                             r= a/2
                             m=2^ (n-1)/2
total no of isomers =a +m
 
e.g for tartaric acid,
        n=2
   a= 2^ (2-1) = 2
   m = 1
thrfore total no of optical isomers = 3


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