i am a bit confused how to calculate total no . of isomers..
for eg if compound shows optical+geometrical isomerism
then how do we count them
i mean do cis and trans diff and are counted separately
and what about distereomers and meso ?
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2 Answers
19Some Golden Rules In Isomerism:
total number of geometrical isomers in polyenes
(1) 2n---->when terminal groups or atoms are different on both sides (n-->no of double bonds)(e.g. 2,4 heptadiene has 22=4 isomers
(2) 2n-1+2n/2 - 1------->when terminal groups or atoms are same(e.g. 2,4 hexadiene has 21 + 20 =3 isomers
total no of optical isomers of a compound
(1) when the molecule cannot be divided into equal halves and (n) is the number of asymmetric carbon atoms
number of (d) and (l) forms =(a)= 2n
number of meso forms = (m) =20
total number of isomers = (a) +(m)
(2)when the molecule can be divided into equal halves
(i) (n)---->number of asymmetric carbon atoms is even
(d) and (l) isomers =(a) = 2n-1
meso isomers =(m) = 2n/2 - 1
total no of isomers = (a) +(m)
(ii) (n)------>number of asymmetric carbon atoms is odd
(d) and (l) isomers =(a) =2n-1 - 2(n/2 - 1/2)
meso isomers =(m) =2 (n/2 -1/2)
total number of isomers = 2n-1
24a good colection of formulae[6]
but i dont want all these...[2]
i just want to know how to calculate no. of isomers manually...