When two or more compounds have similar molecular formula but different skeletons, these are referred to as chain isomer.
In the following structure.
I. `underset("Butanol-1")(CH_(3) - CH_(2) - CH_(2) - CH_(2) - OH)` II. `CH_(3) . CH_(2). CH_(2). CH_(2). OH`
III. `underset("2-methyl propanol-2")(CH_(3) - underset(OH) underset(|)overset(CH_(3)) overset(|)(C) - CH_(3))` IV. `underset("2-methyl propanol-1")(CH_(3) - underset(CH_(3))underset(|)(CH) - CH_(2) -OH)`