Question

what is the iupac name of an isomer for the following compound? ch₃-ch₂-ch₂-ch₂-ch₃ a 2-methylpropane b 2-methylbutane c cyclopentane d pentene

Explanation:

• The given compound \(CH_3 - CH_2 - CH_2 - CH_2 - CH_3\) is pentane (\(C_5H_{12}\)).
• Isomers have the same molecular formula but different structures.
• For option A: 2 - methylpropane (\(C_4H_{10}\)) has a different molecular formula (\(n = 4\) for \(C\) atoms) than pentane (\(n=5\) for \(C\) atoms), so it is not an isomer.
• For option B: 2 - methylbutane (\(C_5H_{12}\)) has the same molecular formula as pentane (\(C_5H_{12}\)) and a different structure (branched vs straight - chain).
• For option C: cyclopentane (\(C_5H_{10}\)) has a different molecular formula (\(H\) atoms: \(10\) vs \(12\) in pentane) due to the ring structure (loses 2 \(H\) atoms compared to the acyclic alkane with the same number of \(C\) atoms).
• For option D: pentene (\(C_5H_{10}\)) has a double bond (degree of unsaturation), so its molecular formula (\(H\) atoms: \(10\)) is different from pentane (\(C_5H_{12}\)).

Answer:

B. 2 - methylbutane