Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

When the ends of alkene containing $n$ double bonds are different, the number of geometrical isomers is $2^n$. Thus for ${\mathrm{CH}}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{Cl}$. Number of geometrical isomers $=2^2=4$ When the ends of alkene containing $n$ double bonds are same, then the number of geometrical isomers $=2^{n-1}+2^{p-1}$ where $p=\frac{n}{2}$ for even $n$ and $\frac{n+1}{2}$ for odd $n$, thus for ${\mathrm{CH}}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-{\mathrm{CH}}_3$ Number of geometrical isomers $=2^{2-1}+2^{\frac{2}{2}-1}=2^1+2^0=2+1=3$.