Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at themeta position are calledmetadirectors. All metadirectors either havea positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the ortho, meta, and para positions. While all three haveresonance forms,the ortho and para intermediates haveone unfavorable structure eachdue to repelling positive charges onadjacent atoms. However, adjacent atoms do not bear like charges in any of the resonance forms of themetaintermediates. Consequently, the ortho- and para-carbocation intermediates are less stable than themeta-carbocation intermediates. Therefore, substitution ispreferred at the meta position.