Only hydrocarbons containing an aldehyde group (RCHO) or a terminal alkyne (R-C≡C-H) will react with Tollens' reagent, leading to a silver mirror formation or a white precipitate, respectively. Aldehydes are oxidized by Tollens' reagent (ammoniacal silver nitrate solution) to form carboxylic acids, while the silver ions (Ag+) are reduced to metallic silver (Ag), which deposits as a silver mirror on the walls of the test tube. 

Terminal alkynes react with Tollens' reagent, producing a white precipitate of silver acetylide.