Question

The total numbers of isomers with molecular formula of ${{\text{C}}_{\text{7}}}{{\text{H}}_{\text{8}}}{\text{O}}$ containing benzene is:
A.$3$
B.$4$
C.$6$
D.$5$

Answer 1

Isomers: They are defined as the molecules which have the same number of molecular formula (i.e. have the same number of atoms of each element) but have different number of structural formulas (i.e. have different structures).

Complete step by step solution:
Let us first talk about what isomers are.
Isomers: They are defined as the molecules which have the same number of molecular formulas (i.e. have the same number of atoms of each element present in the compound) but have different number of structural formulas (i.e. have different structures).
In the question we have to find out the total numbers of isomers with molecular formula of ${{\text{C}}_{\text{7}}}{{\text{H}}_{\text{8}}}{\text{O}}$ containing benzene. Now we know that benzene is a compound having molecular formula ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}}$. And when any group is attached to the benzene ring then one hydrogen atom is eliminated and that group is attached. So the number of carbon atoms remaining are $1$ , hydrogen $3$ and oxygen $1$. The functional group (i.e. the groups which have elements other than carbon and hydrogen) which can be formed using one carbon, one oxygen and three hydrogen can be methyl alcohol, ether (i.e. methoxy benzene) and ortho, meta and para substituted phenols.
Ortho-compounds: In benzene rings if the two functional groups are attached at positions $1$ and $2$ then the compound is known as ortho-compound.
Meta-compounds: In benzene rings if the two functional groups are attached at positions $1$ and $3$ then the compound is known as meta-compound.
Para-compounds: In benzene rings if the two functional groups are attached at positions $1$ and $4$ then the compound is known as para-compound.
The compounds may be:



So, the total numbers of isomers with molecular formula of ${{\text{C}}_{\text{7}}}{{\text{H}}_{\text{8}}}{\text{O}}$ containing benzene is five.

Hence, option (D) is correct.

Note: Cresol is the compound in which the benzene ring is attached to one methyl group. Phenol is compound in which the benzene ring is attached to one hydroxyl group i.e. $- OH$. Ether is the functional group which has a general formula $R - O - {R'}$, where $R$ is any alkyl group and ${R'}$ is also an alkyl which may be the same or different from $R$.