Answer to Question #128855 in Organic Chemistry for Zainab bilal

Question

Why Halogens are deactivating but Ortho para directing

Answer 1

Solution.

Halogens deactivate the benzene ring, but are ortho-and para-orientants, because they have a weak positive mesomeric effect due to their non-white electron pairs. At the same time, they have a fairly strong negative inductive effect, which prevails over the positive mesomeric effect and slows down the electrophilic substitution in any position of the ring, but in the ortho - and para-positions - not too much because of the stabilizing effect of n-p coupling.

Answer:

Halogens deactivate the benzene ring, but are ortho-and para-orientants, because they have a weak positive mesomeric effect due to their non-white electron pairs. At the same time, they have a fairly strong negative inductive effect, which prevails over the positive mesomeric effect and slows down the electrophilic substitution in any position of the ring, but in the ortho - and para-positions - not too much because of the stabilizing effect of n-p coupling.