Isomerism is the existence of chemical compounds that have the same molecular formulae but different molecular structures or different arrangements of atoms in space. Isomers are chemical compounds with the same molecular formula. Isomers may be considered distinct compounds with different physical and/or chemical properties. The nature and significance of these differences depends on the isomers in question. Isomerism is encountered frequently in organic chemistry because of the many ways carbon atoms can form chains and rings.