When 3-methyl-1-phenylpropanal is heated with Tollen's reagent ammoniacal silver nitrate , the aldehyde group in the compound is oxidized to a carboxylic acid group. The product obtained is 3-methyl-1-phenylpropanoic acid. Additionally, silver ions in the Tollen's reagent are reduced to metallic silver, which forms a silver mirror on the walls of the reaction vessel.