What is the relation between the two compounds ${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}$ and  ${\mathrm{CH}}_3-\mathrm{C}\equiv \mathrm{C}-{\mathrm{CH}}_3$?

${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}$ and  ${\mathrm{CH}}_3-\mathrm{C}\equiv \mathrm{C}-{\mathrm{CH}}_3$  have same molecular formula C₄H₆ but the position of the functional group is different. In the first compound, the position of the functional group is 1 while that in the second compound is 2. So they are called position isomers.