See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 – Identify the structure. The compound has a C=C double bond. The left sp2 carbon bears a Cl substituent and a CH3 group. The right sp2 carbon bears a CH2CH3 (ethyl) group and an I substituent. Step 2 – Number the chain. The longest carbon chain that includes the double bond is: CH3–C(Cl)=C(I)–CH2–CH3, which is a 5-carbon chain (pentene). Numbering from the end that gives the double bond the lowest locant: C1=CH3, C2=C(Cl), C3=C(I), C4=CH2, C5=CH3. The double bond is between C2 and C3, so this is pent-2-ene. Substituents: Cl at C2, I at C3 → 2-chloro-3-iodo-2-pentene. Step 3 – Assign cis/trans (geometric isomerism). On C2: the two groups are CH3 and Cl. On C3: the two groups are I and CH2CH3. For cis/trans nomenclature, compare the higher-priority (or simply the identical-type) groups. Using the older cis/trans convention on the main chain carbons: the CH3 (part of the main chain on C2 side) and the CH2CH3 (part of the main chain on C3 side) are on opposite sides of the double bond (trans to each other), because Cl is on the same side as CH2CH3 and I is on the same side as CH3 — examining the structure, Cl is above-left and CH2CH3 is above-right (same side), while CH3 is below-left and I is below-right (same side). Therefore, the two chain carbons (CH3 at C2-end and CH2CH3 at C3-end) are on opposite sides → trans configuration. Step 4 – Full name: trans-2-chloro-3-iodo-2-pentene. Step 5 – Why other options fail: (b) cis-2-chloro-3-iodo-2-pentene: wrong stereodescriptor. (c) trans-3-iodo-4-chloro-3-pentene: wrong numbering (double bond gets higher locant 3 instead of 2). (d) cis-3-iodo-4-chloro-3-pentene: wrong numbering and wrong stereodescriptor. Therefore, the correct answer is A.