Which of the following compounds are constitutional isomers of $C_4{H}_{10}$ (butane)?

• A. $C_3{H}_8$ and propane
• B. $C_4{H}_{10}$ and cyclobutane
• C. $C_4{H}_8$ and 1-butene
• D. $C_4{H}_{10}$ and 2-methylpropane

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the definition of constitutional isomers. Constitutional isomers have the same molecular formula but different connectivity of atoms. This means they must have the same number of each type of atom but differ in how those atoms are connected.
2. Step 2: Identify the molecular formula of butane, which is \(C\_4H\_{10}\). Any constitutional isomer of butane must also have the formula \(C\_4H\_{10}\).
3. Step 3: Examine each given compound's molecular formula and compare it to butane's formula. For example, propane is \(C\_3H\_8\), which differs in the number of carbons and hydrogens, so it cannot be a constitutional isomer of butane.
4. Step 4: Consider cyclobutane, which has the formula \(C\_4H\_8\). Since it has fewer hydrogens than butane, it is not a constitutional isomer but rather a different type of compound (a cycloalkane).
5. Step 5: Look at 2-methylpropane, which has the same molecular formula as butane (\(C\_4H\_{10}\)) but a different connectivity (branched instead of straight chain). This makes 2-methylpropane a constitutional isomer of butane.