See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Periodic acid (HIO4) cleaves vicinal diols (1,2-diols) — compounds that have two hydroxyl groups on adjacent (neighboring) carbon atoms. The mechanism requires the two OH groups to be on adjacent carbons so that a cyclic periodate ester intermediate can form. Step 1 — Establish the rule: HIO4 cleaves only vicinal (1,2-diol) relationships. Any compound lacking OH groups on adjacent carbons will NOT be cleaved. Step 2 — Analyze each compound: I. Glycerol (propane-1,2,3-triol): HO-CH2-CH(OH)-CH2-OH. It has vicinal diol units (C1–C2 and C2–C3 are adjacent OH pairs). Therefore glycerol IS cleaved by HIO4. II. Glycol (ethane-1,2-diol): HO-CH2-CH2-OH. The two OH groups are on C1 and C2 (adjacent). Therefore glycol IS cleaved by HIO4. III. 1,3-propenediol (propane-1,3-diol): HO-CH2-CH2-CH2-OH. The two OH groups are on C1 and C3, which are NOT adjacent carbons. No cyclic periodate ester can form. Therefore 1,3-propenediol is NOT cleaved by HIO4. IV. Methoxy-2-propanol (1-methoxy-2-propanol): CH3-O-CH2-CH(OH)-CH3. One group is an ether (methoxy), not a free hydroxyl. There is only one OH group, so no vicinal diol relationship exists. Therefore methoxy-2-propanol is NOT cleaved by HIO4. Step 3 — Identify compounds NOT cleaved: III and IV. Step 4 — Why other options fail: (a) I, II, III, IV — incorrect because I and II are cleaved. (b) I, II — incorrect because I and II are both cleaved, not uncleaved. (c) II, III — incorrect because II (glycol) is cleaved. Therefore, the correct answer is D.