Constitutional isomers are compounds that have the same molecular formula but different connectivity.
To determine whether two molecules are constitutional isomers, just count the number of each atom in both molecules and see how the atoms are arranged.
If both molecules have the same count for all of the different atoms, and the atoms are arranged in different ways (i.e. their connectivity is different), then they will be constitutional isomers.
In this case C2H5Cl will not have any constitutional isomer. Because you can attach the Cl on first carbon or second carbon, both structure will be same. There will only exist one structure. Figure is attached
