Why ketones do not give Tollens test?

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Detailed Solution

Ketones do not give Tollens test because they lack the –CHO (aldehyde) group needed to reduce Ag⁺ to silver.

The Tollens reagent contains silver ammoniacal complex [Ag(NH₃)₂]⁺ which is an oxidizing agent.
It oxidizes aldehyde groups (–CHO) to carboxylate (–COO⁻), while reducing Ag⁺ to metallic silver (Ag(s)).
Ketones have the general formula R–CO–R′; there is no hydrogen attached to the carbonyl carbon, so they can’t be oxidized further under mild conditions.
Hence, ketones fail to reduce Tollens reagent and no silver mirror or precipitate is seen.
Exception: α-hydroxy ketones (i.e. ketone adjacent to –OH) may sometimes reduce Tollens because they tautomerize to aldehyde or act like reducing groups.

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