Functional Isomerism: This type of isomerism is due to the presence of different functional groups in compounds having the same molecular formula. For example, 2n+2 (a) Both alcohols and ethers have the same general formula C. H. O but differ in the nature of functional groups. For instance, C, HO represent the following two compounds. CH-CH-OH Ethyl alcohol CH,OCH Dimethyl ether