1) if the molecule is unsymetrcl

no.of enantiomeric frms(x)=2ⁿ

no.of meso forms(y)=0   

 

total no. f stereoisomers=x+y

 

2) if the molecule is symetrcl & n is evn

no.of enantiomeric frms(x)=2^(n-1)

no.of meso forms(y)= 2^(n/2)-1

total no. f stereoisomers=x+y

  

 

 

3) if the molecule is symetrcl & n is odd

 

no.of enantiomeric frms(x)=2^(n-1)-2^(n-1/2)

no.of meso forms(y)=  2^(n-1/2)

total no. f stereoisomers=x+y

 

But if u wnt structural isomers, then u wl hve 2 do it by trial & error method.