Given the following pair of structures, indicate the relationship between them: Structure 1: $C_4{H}_{10}$ (n-butane) and Structure 2: $C_4{H}_{10}$ (isobutane).

• A. They are stereoisomers.
• B. They are constitutional isomers.
• C. They are identical compounds.
• D. They are not isomers.

Answer: (B)

Verified step by step guidance

1. Step 1: Identify the molecular formula of both compounds. Both n-butane and isobutane have the formula \(C_4H_{10}\), indicating they are isomers since they share the same molecular formula but differ in structure.
2. Step 2: Understand the difference between types of isomers. Constitutional (or structural) isomers differ in the connectivity of atoms, while stereoisomers have the same connectivity but differ in spatial arrangement.
3. Step 3: Analyze the structures of n-butane and isobutane. n-Butane is a straight-chain alkane, whereas isobutane (also called methylpropane) is a branched-chain alkane. This means their atoms are connected differently.
4. Step 4: Since the connectivity of atoms differs between n-butane and isobutane, they cannot be stereoisomers or identical compounds. They are constitutional isomers because they have the same molecular formula but different connectivity.
5. Step 5: Conclude that the correct relationship between n-butane and isobutane is that they are constitutional isomers.