On the topic of nucleophilic aromatic substitution (S$_N$Ar) reactions, the benzyne mechanism is discussed. When considering the position of substitution, electronic and steric factors are mentioned. When considering electronic factors, effects of substituents on the ring are viewed rather differently, compared to how they are viewed in the conventional electrophilic aromatic substitution reaction.

Pg. 525 from Organic Chemistry (2nd ed.) shows the following diagram:

Pg. 525 of the book in Reference

In the discussion of the benzyne mechanism, conventionally electron-donating groups are said to not be able to exert their donating effects and are even viewed as electron-withdrawing via the inductive effect. However, I cannot see why they behave in this way. Why is their donating effect no longer significant? Certainly, their p orbitals are still in conjugation with the rest of the $\pi$ system right?

However, if their electron-donating effects were more important, then we would observe ortho and para attack by the nucleophile, so as to generate the negative charge at the meta position, which is apparently not the case as experimentally observed.


Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc


2 Answers 2


the electron pair that is creating negative charge on ring is sp2 hybridized and its orbital direction is away from the pi orbital electronic cloud of benzene ring so not able to resonate along with pi electrons. OMe inductively stabilize this electron pair as it is electron with-drawing inductively. thats why NH2 group attaches at meta position rather than ortho position.


The electron-donating effect only affects orbitals which are parallel to the orbital of the lone pair on O. But the orbital, in which the negative charge on benzyne is located, is perpendicular to the other p orbitals. This means there is no overlap, and therefore no conjugation with the lone pair on O.


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