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Mech 41 were us Suggested solutions for Chapter 41 whole in th Problem 1 Propose three fundamentally different mechanisms (other than variations of the same mechanism with different kinds of catalysis) for this reaction. How would (a) D labelling and (b) labelling help to distinguish the mechanisms? What other experiments would you carry out to eliminate some of these mechanisms? O₂N NaOH CO2 0 H2O Other Purpose of the problem to see Investigating a reaction where there are serious doubts about the mechanism. so that and stud Suggested solution - The reaction is an ester hydrolysis so the obvious mechanism is to attack the carbonyl group hydroxide (p. 291). Notice that we draw out each stage and do not use any summary or shorth mechanisms. mechanism 1: normal ester hydrolysis Expla O₂N O₂N O₂N OH CO 0 0 OH But the ester group is attached to an aromatic ring with a para nitro group. Nucleop: substitution on the aromatic ring (p. 591) would give the same product. mechanism 2: nucleophilic aromatic substitution Purpos combi N N O₂N Sugges o 0 0 The OH OH ends of Finally, the CH₂ group between the carbonyl group and the benzene ring is acidic and can with hydroxide as base to form an enolate. Elimination gives a ketene that can be attacked hydroxide acting as a nucleophile to give the product. mechanism 3: enolate elimination to give a ketene HO H H OH O₂N 0 0 a 0 The 0 H H The OH O₂N CO2H or 0 OH