See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: Periodic acid (HIO4) cleaves vicinal diol (1,2-diol) units, and also cleaves alpha-hydroxy aldehydes, alpha-hydroxy ketones, and 1,2,3-triols (consuming 2 moles per triol). Each pair of adjacent OH groups (or adjacent OH and CHO/CH2OH) consumes one mole of HIO4. Step 1: Identify the structure. The compound is methyl glucopyranoside (a cyclic acetal/glycoside). The structure is a six-membered pyranose ring: C1 has OMe (acetal carbon, no free OH), C2-OH, C3-OH, C4-OH, C5 is the ring carbon (no OH), and C6 is CH2OH. Step 2: Since C1 bears an OMe group (it is an acetal/glycoside), it is NOT a free hemiacetal. The ring oxygen connects C1 and C5. C5 has no OH. C6 has CH2OH. Step 3: Count vicinal diol pairs available for HIO4 cleavage. HIO4 cleaves between carbons bearing OH groups (or OH and the equivalent). The free hydroxyl groups are at C2, C3, C4, and C6 (as CH2OH). C1 has OMe (not OH), C5 has no OH. Step 4: Opening the ring for analysis. In periodate oxidation of a glycoside, the ring must be considered open or the vicinal diols within the ring are counted. For methyl glucopyranoside: - C1 (OMe, acetal) - C2 (OH): C1 is not a free OH carbon, so no cleavage between C1 and C2 in the acetal sense. - C2 (OH) - C3 (OH): vicinal diol → consumes 1 HIO4 - C3 (OH) - C4 (OH): vicinal diol → consumes 1 HIO4 - C4 (OH) - C5 (ring O, no OH): no cleavage - C5 - C6 (CH2OH): C5 has no OH, so no cleavage here Step 5: However, the ring oxygen linkage at C1-O-C5 means the hemiacetal is protected. For methyl glycosides, periodate oxidation cleaves only the free vicinal diols. For methyl alpha-D-glucopyranoside, the known result is that it consumes 2 moles of HIO4: one for C2-C3 diol and one for C3-C4 diol, giving one mole of formic acid (from C3) and fragmenting the chain. Step 6: The maximum value of x is 2, corresponding to cleavage of the C2-C3 and C3-C4 vicinal diol pairs. Why other options fail: - (a) 1: undercounts; there are two vicinal diol pairs - (c) 3: would require an additional vicinal diol pair not present - (d) 4: far exceeds available vicinal diol pairs Therefore, the correct answer is B.