See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 (Identify the principal functional group): The structure contains a terminal aldehyde (CHO) group, so the parent chain must end in -al. Step 2 (Find the longest carbon chain including the aldehyde carbon): Starting from the aldehyde carbon (C1) and tracing the longest continuous chain: C1(CHO)-C2-C3-C4-C5-C6-C7-C8. The chain at C5 has a branch; we must include whichever direction gives the longer chain. From C5 one path goes C6-C7-C8 (3 carbons) and the branch is a single methyl group. So the longest chain through C5 going to C8 gives 8 carbons total: octanal as the base name. Step 3 (Number the chain): The aldehyde carbon is always C1. Counting from C1: C1(CHO), C2, C3, C4, C5(branch), C6, C7, C8. The methyl branch is located at C5. Step 4 (Name the substituent): The branch at C5 is a single -CH3 group, named methyl. Step 5 (Assemble the IUPAC name): substituent position + substituent name + parent chain = 5-methyl + octan + al = 5-methyloctanal. Step 6 (Verify): The molecular formula check: 8-carbon chain (octanal) + 1 methyl branch = C9H18O, consistent with the drawn structure. Therefore, the correct answer is 5-methyloctanal.