Answer. It is a phenomenon in which compounds have same molecular formula but different structural formulae. These different structures are called isomers. Isomers have the same molecular formula but different arrangement of atoms in molecules or different structural formulae. Isomerism also adds to the possible number of structures, e.g., molecular formula C5H12 can be represented by three different structures. Thus, C5H12 has three isomers, as shown below:
CH3
H3C-CH2-CH2-CH2- CH3 H3C-CH-CH2-CH3 H3C-C-CH3
CH3 CH3 CH3
n-pentane isopentane neopentane