The number of structural isomers for C 6 H 14 is:

Firstly we calculate DU (Degree of unsaturation) of given molecular formula as :-

$\mathrm{DU}=\left(\mathrm{C}+1\right)-\left(\frac{\mathrm{H}+\mathrm{X}-\mathrm{N}}{2}\right)$

for ${\mathrm{C}}_6{\mathrm{H}}_{14}$

$\mathrm{DU}=\left(6+1\right)-\left(\frac{14}{2}\right)=0$

$\therefore$ possibility is for alkanes only.

(PCC stands for parent carbon chain)

$\therefore$ Total structural isomers of ${\mathrm{C}}_6{\mathrm{H}}_{14}$ are $5$.