Question

What products are obtained from the reaction of the following compounds with one equivalent of ${\mathbf{Br}}_2$, using${\mathbf{FeBr}}_3$as a catalyst?

a.

b.

c.

d.

Short answer

a.

b.

c.

d.

Step-by-step solution

Step-by-step-solutionStep 1: Direction of substituents

All activating substituents direct an incoming electrophile to the ortho and para positions. The weakly deactivating halogens also direct an incoming electrophile to the ortho and para positions . All moderately and strongly deactivating substituents direct an incoming electrophile to the meta position.

Formation of the products

a)

The Methoxy group is more highly active toward electrophilic substitution reaction than the methyl group because oxygen donates electrons by mesomeric effect. Therefore, the ring on the right undergoes an electrophilic substitution reaction.

Formation of the desired product (a)

b)

The left side of the ring is attached to an electron-donating group and the right side of the ring is attached to an electron-withdrawing group which deactivates the ring so the reaction occurs as follows:

Formation of the desired product (b)

c)

The ring on the right side is activated by the donation of oxygen lone pair of electrons by mesomeric effect. Therefore, the ring on the right undergoes an electrophilic substitution reaction.

Formation of the desired product (c)

d)

The ring on the left side is activated by the donation of oxygen lone pair of electrons by mesomeric effect whereas on the right side is deactivated by the electron-withdrawing nature of nitro group by resonance, Therefore, the substitution reaction.

Formation of the desired product (d)