See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1: Identify the structure. The molecule has a main chain: CHO — CH = CH — CH2 — CHO, where a CHO group is attached to the CH2 carbon (the carbon bearing CH2 also has a CHO substituent). Let us re-read: CH2 — CH = CH — CHO with a CHO hanging off the CH2. So the full structure is: OHC — CH2 — CH = CH — CHO. This gives us five carbons in the chain if we count both aldehyde carbons as part of the chain. Step 2: Number the longest carbon chain containing both aldehyde groups. The chain is: C1(CHO) — C2(CH2) — C3(CH=) — C4(=CH) — C5(CHO). Wait, let me recount: the CHO groups themselves are the terminal carbons. So the chain is: C1 = CHO, C2 = CH2, C3 = CH, C4 = CH, C5 = CHO, with a double bond between C3 and C4. That gives a 5-carbon chain (pent) with aldehyde groups at C1 and C5 (dial) and a double bond between C2 and C3, or between C3 and C4 depending on numbering direction. Step 3: Apply lowest locant rule for the double bond. Numbering from left (the CH2 end): C1 = CHO (from the branch), but aldehyde carbons must be C1 and C5. Number so that the double bond gets the lowest possible locant. If we number: C1(CHO) — C2(CH2) — C3(CH=) — C4(=CH) — C5(CHO), the double bond is at C3 (pent-3-ene). If we number from the other end: C1(CHO) — C2(CH=) — C3(=CH) — C4(CH2) — C5(CHO), the double bond is at C2 (pent-2-ene). The lowest locant for the double bond is 2, so we use pent-2-ene-1,5-dial. Step 4: Name the compound. Parent chain: pentane (5 carbons). Suffix: dial (two aldehyde groups at C1 and C5). Double bond: between C2 and C3, giving ene with locant 2. Full name: Pent-2-ene-1,5-dial. Step 5: Eliminate other options. (a) propene-1,3-dial — only 3 carbons, incorrect chain length. (b) Propene-1,3-dicarbaldehyde — incorrect, implies additional CHO groups outside the chain. (c) Pent-3-ene-1,5-dial — uses locant 3 for the double bond, but locant 2 gives a lower number, so this violates the lowest locant rule. Therefore, the correct answer is D.