Video Transcript
Which of the following molecules
are used by chemists to prepare benzene through cyclic polymerization reactions? (A) Ethane, (B) ethyne, (C)
ethanol, (D) ethanoic acid, or (E) ethene.
Benzene is a hydrocarbon with a
molecular formula of C6H6. The six carbon atoms are joined in
a cyclic ring. Here, we represented benzene with
alternating single and double bonds between the carbon atoms. But benzene is often represented by
a skeletal formula like this, where the circle indicates that the electrons in the
ring are actually delocalized over the six carbon atoms.
Benzene can be prepared in a number
of ways. One common method is cyclic
polymerization. During cyclic polymerization,
similar chemical units called monomers join together to form a structure with a
closed ring. The monomer used for the cyclic
polymerization reaction to form benzene is the two-carbon alkyne ethyne. The ethyne is passed through a
red-hot iron tube or a red-hot nickel tube at 873 kelvin. Under these conditions, electrons
in an ethyne molecule can rearrange to form new bonds with other ethyne
molecules. The formation of new bonds turns
three ethyne molecules into a single benzene molecule.
In conclusion, the molecule used by
chemists to prepare benzene through cyclic polymerization reactions is ethyne,
answer choice (B).
