How would you rank the following aromatic compounds in order of their reactivity in electrophilic aromatic substitution: anisole, nitrobenzene, acetophenone, toluene, and benzene?

Question

Emilia Alvarez · Accepted Answer

The aromatics may be ordered on the basis of electron donating groups substituting the phenyl ring. Now excuse me while I find out what anisole is.

The terms "mesomeric effect" and "inductive effect" refer to the removal of electron density from the ring by electronegative atoms and the delocalization of lone pairs on the substituent, which increases the ring's electron content and reactivity. Phenyl ethers, phenols, and anilines are significantly more reactive than benzene because, despite oxygen and nitrogen being electronegative with respect to carbon, the lone pairs on the neutral atom can be decoupled around the ring. Phenol, in particular, does not even require a Lewis acid to undergo bromination. On the other hand, the presence of a quaternized nitrogen (i.e. #NH_3^+# or a nitro group, #-{N^(+)(=O)O^-}# strongly deactivates the ring towards substitution. Carbonyl groups, in which the ipso carbon has a partial positive charge are deactivating. Alkyl (methyl) or hydrocarbyl substitution also lends electron density to the ring. Thus, the following is a rough list of reactivity in electrophilic substitution: I strongly advise you to look at the many data on real experiments that are available online and in your text. Nitrobenzene, acetophenone, benzene, toluene, and anisole are the most reactive species under these circumstances.

Ava Andrews · Answer

undefined The ranking of aromatic compounds in terms of reactivity in electrophilic aromatic substitution generally follows the electron-donating or withdrawing abilities of substituents. In this case:

1. Toluene (methyl group is electron-donating, enhancing reactivity)
2. Anisole (methoxy group is electron-donating, similar to toluene)
3. Benzene (no substituent, moderate reactivity)
4. Acetophenone (carbonyl group is weakly electron-withdrawing, slightly reducing reactivity)
5. Nitrobenzene (nitro group is strongly electron-withdrawing, significantly reducing reactivity)