Which of the following pairs of compounds are constitutional isomers of each other?

• A. $C_4{H}_{10}$: n-butane and isobutane
• B. $C_2{H}_6$: ethane and ethanol
• C. $C_5{H}_{12}$: n-pentane and neopentane
• D. $C_3{H}_8$: propane and cyclopropane

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definition of constitutional isomers. Constitutional isomers are compounds that have the same molecular formula but different connectivity of atoms, meaning their atoms are connected in different orders.
2. Step 2: For each pair, compare their molecular formulas. If the formulas differ, they cannot be constitutional isomers. For example, ethane (C\\_2H\\_6) and ethanol (C\\_2H\\_6O) have different molecular formulas, so they are not constitutional isomers.
3. Step 3: For pairs with the same molecular formula, analyze their structures to confirm different connectivity. For example, n-butane and isobutane both have the formula C\\_4H\\_10 but differ in the arrangement of carbon atoms, making them constitutional isomers.
4. Step 4: Consider cyclic versus acyclic structures. For example, propane (C\\_3H\\_8) and cyclopropane (C\\_3H\\_6) have different molecular formulas due to the ring structure affecting hydrogen count, so they are not constitutional isomers.
5. Step 5: Summarize by identifying pairs with identical molecular formulas but different connectivity as constitutional isomers, such as n-butane and isobutane (C\\_4H\\_10), and n-pentane and neopentane (C\\_5H\\_12).