See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1: Identify the structure. The molecule shown is CH2=CH-CH(CH3)-CH2-CHO. It contains a terminal aldehyde group (-CHO), a methyl branch, and a terminal alkene (vinyl group). Step 2: Identify the principal characteristic group. The aldehyde (-CHO) is the principal characteristic group and gets the lowest possible locant. In IUPAC nomenclature, the carbon of the aldehyde is C-1. Step 3: Number the chain. The longest chain that includes both the aldehyde carbon and the double bond: C1(CHO)-C2(H2)-C3(H)(CH3)-C4(H)=C5(H2) So: CHO is C1, CH2 is C2, CH(CH3) is C3, CH= is C4, =CH2 is C5. Step 4: Name the compound. The parent chain has 5 carbons → pentanal (since -CHO is at C1, suffix is -al). The double bond is between C4 and C5 → pent-4-enal. The methyl branch is at C3 → 3-methylpent-4-enal. Step 5: Evaluate the options: (a) 3-Methylpent-1-en-4-al: This would imply the double bond is at C1 and the aldehyde is at C4, which is incorrect numbering since aldehyde must be C1. (b) 3-Methylpent-4-enal: Correct - aldehyde at C1, double bond at C4-C5, methyl at C3. (c) 3-Methylpent-4-carbaldehyde: 'carbaldehyde' suffix is used when the CHO carbon is not part of the main chain (e.g., cyclopentanecarbaldehyde); incorrect here. (d) 3-Methyl-5-oxopent-1-ene: This names the aldehyde as 'oxo' substituent and numbers from the alkene end, which is incorrect since aldehyde has higher priority. Therefore, the correct answer is B.