Recognize structural isomers

Define structural isomers as formula, but different structural formulae, including $\mathrm{C}_{4} \mathrm{H}_{10}$ as $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$ and $\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2}$ and $\mathrm{C}_{4} \mathrm{H}_{8}$ as $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}^{-} \mathrm{CH}_{2}$ and $\mathrm{CH}_{3} \mathrm{CH}^{-} \mathrm{CHCH}_{3}$