Carbonyl Chemistry and Reactivity (5D) Practice Test

A peptide chemist attempts to protect a ketone-containing side chain during a multi-step aqueous synthesis. The compound contains a simple ketone (R–CO–R') and is treated with ethylene glycol (excess) and catalytic p-toluenesulfonic acid in toluene under reflux with water removal. The central concept is acetal (ketal) formation via nucleophilic addition to carbonyls. Which product is most likely formed from the reaction described?

A formulation scientist tests reversible covalent inhibition via carbonyl chemistry. A protease is incubated with an electrophilic inhibitor containing either a nitrile (R–C≡N) or an aldehyde (R–CHO). Under identical aqueous conditions (pH 7.4, 37°C), the aldehyde inhibitor shows time-dependent loss of enzyme activity that is partially reversed upon dilution, consistent with a reversible covalent adduct at the active-site serine. The central concept is nucleophilic addition to carbonyls. Which adduct is most consistent with serine attacking the aldehyde?