Given two compounds with the molecular formula $C_4{H}_{10}$, one being n-butane and the other isobutane, what is the relationship between these two structures?

• A. They are constitutional isomers.
• B. They are stereoisomers.
• C. They are identical compounds.
• D. They are tautomers.

Answer: (A)

Verified step by step guidance

1. Step 1: Identify the molecular formula of both compounds, which is given as \(C_4H_{10}\). This means both compounds have the same number and type of atoms.
2. Step 2: Recognize the names of the compounds: n-butane and isobutane. These names indicate different structural arrangements of the same molecular formula.
3. Step 3: Understand that n-butane is a straight-chain alkane, while isobutane (also called methylpropane) is a branched-chain alkane. This difference in connectivity means their atoms are connected differently.
4. Step 4: Recall the definition of constitutional (or structural) isomers: compounds with the same molecular formula but different connectivity of atoms. Since n-butane and isobutane differ in connectivity, they fit this definition.
5. Step 5: Differentiate from other types of isomers: stereoisomers have the same connectivity but differ in spatial arrangement; tautomers involve rapid equilibrium between isomers differing in proton position and double bonds; identical compounds are the same molecule. Therefore, n-butane and isobutane are constitutional isomers.