isomeric \i`so*mer"ic\ ([imac]`s[-o]*m[e^]r"[i^]k), a. [Iso- +
Gr. me`ros part: cf. F. isom['e]rique.] (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.
[PJC]
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."
[1913 Webster]
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