Question

The number of aromatic isomers possible for ${C_7}{H_8}O\;$ is:

Answer 1

Isomerism is a phenomenon of organic chemistry in which more than one species has the same chemical formula but different structures. Those compounds that have the same chemical formula but different properties and the arrangement of atoms in their molecule are called isomers.

Complete answer:
In aromatic isomerism, the basic structure is benzene whose molecular formula is ${C_6}{H_6}$ and the rest of the atoms are placed differently on the ring forming different isomers with the same atoms. Here we are given the molecular formula ${C_7}{H_8}O\;$ and the benzene ring formula which is ${C_6}{H_6}$, so the remaining atoms we have is $1$ C$,$2 $H$ and $1$ $O$ atom. ${C_7}{H_8}$ is toluene. It’s the only benzenoid isomer that is possible. Now we have to insert $1$ $O$ atom into the ring. We can do that in five ways.
we can arrange the $C{H_3}$ and $O$ atom on the ortho, para, and meta position, that will get us $2 - methylphenol$ , $3 - methylphenol$ and $4 - methylphenol$ . The common names of these compounds are $o - cresol,\,m - cresol$ and $p - cresol$. One way is that if we place the oxygen atom with the methyl group which will lead to the formation of methyl phenyl ether also known as anisole. The fifth isomer could be benzyl alcohol in which $- OH$ group is attached to the $C{H_2}$ group. Hence, in this way, we can say that the possible isomers for the molecular formula ${C_7}{H_8}O\;$ will be five. These are:

Note:
Isomerism is of two types (a) Structural and (b) Stereo. Aromatic isomerism is a type of structural isomerism. In structural isomerism, the molecular formula of every compound is the same but has different placement of bonds and atoms in the molecule.