what is the relative bromination rates of the following aromatic compounds; clorobenzene, methoxybenzene, nitrobnzene, toluene, benzene
To determine the relative bromination rates of the aromatic compounds mentioned (chlorobenzene, methoxybenzene, nitrobenzene, toluene, and benzene), we need to consider their electronic and steric effects.
1. Chlorobenzene: Chlorobenzene is a relatively poor director for electrophilic aromatic substitution reactions due to the electron-withdrawing effect of the chlorine atom. This makes it less reactive compared to benzene. Therefore, its bromination rate would be relatively slower compared to the other compounds.
2. Methoxybenzene (Anisole): Methoxybenzene contains a methoxy (-OCH3) group, which is an electron-donating group. This methoxy group is an ortho/para director and increases the electron density on the aromatic ring, making it more reactive towards electrophilic substitution. Thus, the bromination rate of methoxybenzene would be faster than that of chlorobenzene.
3. Nitrobenzene: Nitrobenzene features a nitro group (-NO2), which is a strong electron-withdrawing group. The nitro group withdraws electron density from the ring, making it a meta director and decreasing the electron density at the ortho and para positions. Therefore, nitrobenzene is less reactive towards electrophilic substitution reactions. Consequently, its bromination rate would be slower compared to the other compounds.
4. Toluene: Toluene carries a methyl group (-CH3) as a substituent. This group is weakly electron-donating and has a modest ortho/para directing effect. Although it increases the electron density on the aromatic ring, it is not as strong as the methoxy group in methoxybenzene. Thus, the bromination rate of toluene would be slower than that of methoxybenzene but faster than chlorobenzene and nitrobenzene.
5. Benzene: In the absence of any substituents, benzene is the most reactive among the given compounds. It does not possess any electron-withdrawing or electron-donating groups that would modify its reactivity. Therefore, benzene has the highest bromination rate compared to the other compounds.
In summary, the relative bromination rates from fastest to slowest would be:
Benzene > Methoxybenzene > Toluene > Chlorobenzene > Nitrobenzene