Question

In the bromination of arenes, which of the following statements regarding the reaction is true?a.The hydrocarbon is used in excess.spaceb.Equimolar quantities of bromine and the hydrocarbon are used.spacec.Bromine is used in excess.spaced.Stoichiometry does not matter in this experiment since we are only interested in the rate of the reaction.

Answer 1

The hydrocarbon is used in excess.

Explanation:

The bromination of an arene is not simple as bromination of an alkane. This is because the carbocation or free radicle formation in benzene is a very energy consuming process. This is why a lewis base like aluminium bromide or ferric bromide is used. The ferric bromide takes in the bromine radicle and forms the brominium cation which helps in the formation of electrophile. Now this electrophile brominium cation attacks the benzene ring and forms a temporary sp3 hybrid carbon intermediate. Then the hydrogen is taken by the FeBr4- forming HBr and regenerating the FeBr3 as well as Aromaticity of the arene species at the same time. Here hydrocarbon is used in excess just to prevent the chances of multiple substitution in the same arene molecule.