IIT JEE , AIEEE Forum - Articles Category , Community shelf

magiclko

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