See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: The Pinacol-Diazotization (also called the Tiffeneau-Demjanov or related semipinacol-type rearrangement via diazonium) involves a 1,2-diol system where one OH is replaced by an amino group (NH2), which is then diazotized (using NaNO2/HCl) to form a diazonium ion. The diazonium ion is an excellent leaving group, and the adjacent hydroxyl-bearing carbon facilitates a 1,2-shift (semipinacol-type migration), resulting in a carbonyl compound (ketone or aldehyde). Step 2 - Reasoning for option (b): In option (b), the starting material is Me2C(OH)-CMe2(NH2) (a beta-amino alcohol, i.e., a 1,2-amino alcohol). Treatment with NaNO2/HCl diazotizes the NH2 group to give a diazonium ion on the CMe2 carbon adjacent to the C(OH)Me2 carbon. The nitrogen (N2) then leaves, generating a carbocation, and simultaneously a 1,2-methyl shift from the adjacent carbon bearing the OH group occurs (semipinacol rearrangement). This gives the ketone Me-C(=O)-CMe3 (methyl neopentyl ketone / pinacolone). This is the classic Pinacol-Diazotization (Tiffeneau-Demjanov type) reaction. Step 3 - Why other options fail: - Option (a): Uses Ag+ with a beta-halohydrin. This is a neighboring group or silver-assisted ionization, not Pinacol-Diazotization. - Option (c): Uses H+ with a 1,2-diol (pinacol). This is the classic Pinacol rearrangement, NOT Pinacol-Diazotization. - Option (d): Involves a spiro ketone reacting with H+ — this is a semipinacol rearrangement of a cyclic substrate, not Pinacol-Diazotization. Step 4 - Conclusion: Only option (b) involves the diazotization of an amino alcohol followed by 1,2-shift, which is the definition of Pinacol-Diazotization. Therefore, the correct answer is B.