Question

How many structural isomers are possible for mono bromo benzene?

Answer 1

Hint: The compounds which have the same molecular formula, but the bonds are arranged in a different manner, are termed as structural compounds. In the given molecule, benzene is the parent molecule. It is a six membered cyclic, conjugated ring.

Complete step by step answer:
Benzene is the parent group in the given molecule. It has six carbon atoms and has alternate double bonds. It has a planar structure. The chemical formula of benzene is ${{{C}}_6}{{{H}}_{12}}$. In the given compound, the hydrogen atoms are substituted with other groups like bromine, chlorine. Since it is given that monobromo, there is only one bromine atom and dichloro means two chlorine atoms are substituted in the place of hydrogen atoms.
Thus the structure of the given molecule can be drawn as given below:

We have three substitutions in the benzene ring. When we keep bromine fixed, two chlorine atoms keep changing. So the structures become as follows:
           

Thus we can say that the number of structural isomers are dependent on the number of substitutions. Here, there are three substitutions. Thus the number of structural isomers $ = 2 \times 3 = 6$. So there are six structural isomers present for the given molecule.

Additional information:
Following are the names of the six structural isomers given above:
I- 1-bromo-2,3-dichlorobenzene
II- 1-bromo-2,4-dichlorobenzene
III- 2-bromo-1,4-dichlorobenzene
IV- 2-bromo-1,3-dichlorobenzene
V- 4-bromo-1,2-dichlorobenzene
VI-1-bromo-3,5-dichloro benzene

Note: There are two more structural isomers for the same molecule which is given below:

But these cannot be considered as structural isomers because both of them are similar to compounds III and V respectively.