For geometrical isomers (i.e. in case of polyenes),
If 'n' is even (here n is the number of double bonds):
Number of stereoisomers=2n−1+2n/2−1Number of stereoisomers=2n−1+2n/2−1
If 'n' is odd, then:
Number of stereoisomers=2n−1+2(n−1)/2Number of stereoisomers=2n−1+2(n−1)/2
And for optical isomers (molecules with chiral centres):
If 'n' is even (here n is the number of chiral centres):
Number of enantiomers=2n−1Number of enantiomers=2n−1
Number of meso compounds=2n/2−1Number of meso compounds=2n/2−1
Total number of optical isomers=2n−1+2n/2−1Total number of optical isomers=2n−1+2n/2−1
If 'n' is odd:
Number of enantiomers=2n−1−2(n−1)/2Number of enantiomers=2n−1−2(n−1)/2
Number of meso compounds=2(n−1)/2Number of meso compounds=2(n−1)/2
Total number of optical isomers=2n−1
