Which of the following compounds is a constitutional isomer of $C_8{H}_{18}$?

• A. $C_7{H}_{16}$ (heptane)
• B. $C_8{H}_{18}$ (2,2,4-trimethylpentane)
• C. $C_9{H}_{20}$ (nonane)
• D. $C_8{H}_{16}$ (octene)

Answer: (B)

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.
2. Step 2: Identify the molecular formula of the given compound, which is C\_8H\_18. This means the compound has 8 carbon atoms and 18 hydrogen atoms.
3. Step 3: Examine each option's molecular formula to see if it matches C\_8H\_18. Only compounds with the exact same molecular formula can be constitutional isomers.
4. Step 4: Recognize that heptane (C\_7H\_16) and nonane (C\_9H\_20) have different numbers of carbon and hydrogen atoms, so they cannot be constitutional isomers of C\_8H\_18.
5. Step 5: Note that octene (C\_8H\_16) has the correct number of carbons but fewer hydrogens due to the double bond, so it is not a constitutional isomer of C\_8H\_18. Therefore, 2,2,4-trimethylpentane (C\_8H\_18) is the constitutional isomer because it has the same molecular formula but a different connectivity.