Question

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

Answer 1

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.

Explanation:

Organic chemists speak of an inductive effect, where electronegative atoms withdraw electron density from the ring, and a mesomeric effect, where lone pairs on the substituent are delocalized around the ring making it more electron-rich and reactive.

While oxygen/nitrogen are electronegative with respect to carbon, the lone pairs on the neutral atom can be decoupled around the ring, with the result that phenyl ethers and phenols and anilines are much more reactive than benzene; phenol in particular does not even need 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.

So, tentative order of reactivity in electrophilic substitution:

Nitrobenzene, acetophenone, benzene, toluene, anisole; i.e. anisole is the most reactive species under these conditions. There should be much data on actual experiments on the web, and in your text. I urge you to look at these, and consider the proferred explanations.