Question

Which of the following are correct structural isomers of butane?

1. \[\begin{array}{cc}
   \ce{H}\phantom{...}\ce{H}\phantom{...}\ce{H}\phantom{...}\ce{H}\\
   |\phantom{....}|\phantom{....}|\phantom{....}|\\
   \ce{H - C - C - C - C - H}\\
   |\phantom{....}|\phantom{....}|\phantom{....}|\\
   \ce{H}\phantom{...}\ce{H}\phantom{...}\ce{H}\phantom{...}\ce{H}\\
   \end{array}\]
   
   
2. \[\begin{array}{cc}
   \ce{H}\phantom{...}\ce{H}\phantom{...}\ce{H}\\
   |\phantom{....}|\phantom{....}|\\
   \ce{H - C - C - C - H}\\
   |\phantom{.....}|\phantom{.....}|\\
   \ce{H}\ce{H-C-H}\ce{H}\\
   |\\
   \ce{H}\\
   \end{array}\]
3. \[\begin{array}{cc}
   \ce{H}\phantom{...}\ce{H}\phantom{...}\ce{H}\\
   |\phantom{....}|\phantom{....}|\\
   \ce{H - C - C - C - H}\\
   |\phantom{.....}\backslash\phantom{..}|\\
   \phantom{....}\ce{H}\phantom{......}\ce{C - H}\phantom{}\\
   \phantom{.......}|\\
   \phantom{.......}\ce{H}\\
   \end{array}\]
4. \[\begin{array}{cc}
   \ce{H}\phantom{...}\ce{H}\\
   |\phantom{....}|\\
   \ce{H - C - C - H}\\
   |\phantom{....}|\\
   \ce{H - C - C - H}\\
   |\phantom{....}|\\
   \ce{H}\phantom{...}\ce{H}\\
   \end{array}\]

Options

• (i) and (iii)

• (ii) and (iv)

• (i) and (ii)

• (iii) and (iv)

Answer 1

(i) and (ii)

Explanation  - 

We see that compound (i) and compound (ii) have the same formula C₄H₁₀. Such compounds with identical molecular formula but different structures are called structural isomers.