Question

Predict the major product at the end of each sequence.

(a)

(b)

Short answer

(a) 3-chlorobenzenesulfonic acid

(b) 4-chlorobenzenesulfonic acid

Step-by-step solution

The order of Substitution.

The order of substitution determines the product. To produce the ortho or para product, attaching the o,p-director first is required. Similarly, to produce the meta product, attaching the m-director first is required. In ortho and para mixtures, the para isomer is usually the major product.

Subpart (a) Product of the first reaction sequence.

Here, the first meta-directing group is attached to the ring so that the second substituent gets attached to the meta position forming the product given below.

The chlorination goes at meta-position because the electron-withdrawing sulpho-group (EWG) extracts electron density from ortho and para position.

Subpart (b) Product of the second reaction sequence.

Here first ortho, para-directing group is attached to the ring and in ortho-para mixtures, the para isomer is usually the major product.

Hence, the second substituent gets attached to the para position forming the product given below.