See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1: Identify the full carbon skeleton. The structure is CH3—CH(OH)—CH(C2H5)—CH2—OH. Writing out all carbons: the C2H5 group contributes 2 carbons as a branch (ethyl group). The main chain candidates must be identified. Step 2: Identify the longest carbon chain containing both OH groups. The atoms in the drawn chain are: C1(CH3) — C2(CH-OH) — C3(CH-C2H5) — C4(CH2-OH). That gives a 4-carbon chain with OH at C2 and... wait, let us re-examine. Step 3: Re-read the structure: CH3 — CH(OH) — CH(C2H5) — CH2 — OH. The chain drawn has 4 carbons: C1=CH3, C2=CH(OH), C3=CH(C2H5), C4=CH2OH. The substituent at C3 is an ethyl group (C2H5). Step 4: Check if a longer chain exists by incorporating the ethyl branch. If we include one carbon of the ethyl group into the main chain: chain becomes CH2OH — CH(OH) — CH — CH2 — CH3 with a —CH3 branch at C3, giving 5 carbons. But this gives a methylpentanediol, which is not among the options. Step 5: Number the 4-carbon chain to give lowest locants to OH groups. Numbering from the CH2OH end: C1=CH2OH, C2=CH(C2H5), C3=CH(OH), C4=CH3. OH groups at C1 and C3; ethyl at C2. Name: 2-Ethylbutane-1,3-diol. Step 6: Verify locants. From the other end: OH at C2 and C4 with ethyl at C3 → locant set {2,4} vs {1,3}. The set {1,3} is lower, so numbering from CH2OH end is correct. Step 7: The parent chain is butane (4 carbons), with OH groups at positions 1 and 3, and an ethyl substituent at position 2. IUPAC name: 2-Ethylbutane-1,3-diol. Step 8: Why other options fail: - (a) 3-Ethylbutane-2,4-diol: incorrect numbering direction giving higher locants {2,4}. - (c) 3-Ethylbutane-1,3-diol: ethyl at C3 and OH at C1,C3 — this misplaces the substituent. - (d) 2-Ethyl-1-methylpropane-1,3-diol: propane parent is only 3 carbons; the longest chain containing both OHs is 4 carbons, so butane must be the parent. Therefore, the correct answer is B.