Ammoniacal silver nitrate is used to test for alkynes with terminal hydrogen atoms, which forms a white precipitate due to the formation of silver acetylides. Let us evaluate each option to determine which compound reacts with ammoniacal silver nitrate:
- CH3C≡CH: This compound is known as propyne. It is a terminal alkyne because there is a hydrogen atom attached to the terminal carbon of the alkyne group. Terminal alkynes readily react with ammoniacal silver nitrate to form a white precipitate.
- CH3C≡CCH3: Known as 2-butyne, it is an internal alkyne because the alkyne linkage is between two carbon atoms, both of which are attached to other carbon atoms. Internal alkynes do not form a precipitate with ammoniacal silver nitrate.
- CH3CH=CH2: This compound is propene, an alkene, which does not react with ammoniacal silver nitrate because the selective reaction occurs only with terminal alkynes.
- CH2=CH2: Known as ethene, this is also an alkene, similar to the previous compound, and will not react with ammoniacal silver nitrate.
Thus, the compound CH3C≡CH, being a terminal alkyne, will form a white precipitate when reacted with ammoniacal silver nitrate.