Metamerism This type of isomerism arises due to difference in the distribution of carbon atoms on either side of the functional group in compounds having the same molecular formula. For example, (a) Diethyl ketone and methyl propyl ketone represent a pair of metamers having the molecular formula C, H, O. CH3-CH2-C-CH2-CH3 Diethyl ketone CH3-C-CH2-CH2-CH3 Methyl propyl ketone