isomeric adj. (Chem.) Having the same chemical composition and molecular weight; having the same number of atoms of each kind in the molecule; said of chemical compounds with known chemical composition. This property used to be called metameric to distinguish it from other forms of isomerism. Note: Formerly the term isomeric applied also to comopounds having the same percentage chemical composition, even if the number of atoms in a molecule differed. In the 1913 dictionary isomeric was defined as: "Having the same percentage composition; said of two or more different substances which contain the same ingredients in the same proportions by weight, often used with with. Specif.:
(a)
Polymeric; i. e., having the same elements united in the same proportion by weight, but with different molecular weights; as, acetylene and benzine are isomeric (polymeric) with each other in this sense. See Polymeric.
(b)
Metameric; i. e., having the same elements united in the same proportions by weight, and with the same molecular weight, but with a different structure or arrangement of the ultimate parts; as, ethyl alcohol and methyl ether are isomeric (metameric) with each other in this sense. See Metameric."
