Isomeric /(ī`sō̇*mĕr"ĭk)/

I·so·mer·ic

Isomeric

a.
  1. 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. (Chem.)
  2. 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.