See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify reactive sites toward PhMgBr (a Grignard reagent, a strong nucleophile and strong base). The starting material contains the following functional groups that can react with PhMgBr: 1. The ester group (MeO2C-) on the ring: A Grignard reagent adds twice to an ester. The first equivalent converts the ester to a ketone intermediate; the second equivalent adds to that ketone to give a tertiary alcohol. Since the product shows a -C(Ph)2OH group (two Ph groups on the carbon that was previously the ester carbonyl carbon), exactly 2 equivalents of PhMgBr are consumed at the ester (first addition gives ketone, second addition gives the gem-diphenyl carbinol after workup). Step 2 - Consider the NH group (secondary amine, -NH-tBu): The N-H proton is acidic enough to be deprotonated by the Grignard reagent (which acts as a base). This consumes 1 equivalent of PhMgBr as an acid-base reaction (PhMgBr + R2NH -> PhH + R2N-MgBr). This equivalent is not incorporated into the carbon skeleton but is consumed stoichiometrically. Step 3 - Consider the OH groups: There are two OH groups in the starting material: the benzylic/secondary alcohol (-CH(OH)-) on the side chain and the phenolic OH (HO- on the ring at C4). Both of these acidic protons will react with PhMgBr as a base (acid-base reaction), each consuming 1 equivalent of PhMgBr. - Phenolic OH: 1 equivalent consumed - Secondary alcohol OH (CHOH): 1 equivalent consumed Step 4 - Tally all equivalents: - 1 eq for N-H deprotonation - 1 eq for phenolic O-H deprotonation - 1 eq for secondary alcohol O-H deprotonation - 2 eq for nucleophilic addition to the ester (ester -> ketone -> tertiary alcohol with two Ph groups) Total = 1 + 1 + 1 + 2 = 5 equivalents Step 5 - Verify with product: The product shows the ester converted to -C(Ph)2OH (confirms 2 nucleophilic additions), the two OH and one NH are restored upon aqueous workup (H3O+), consistent with the proton-transfer steps consuming Grignard but being reversed on workup. The net result requires 5 equivalents total. Why other options fail: - 3 equivalents: Would not account for all acidic protons plus both additions to the ester. - 4 equivalents: Misses one of the acidic proton equivalents or one of the ester additions. - 6 equivalents: Overcounts; there is no additional reactive site requiring a 6th equivalent. Therefore, the correct answer is C.