Isomerism involving the same atoms in different arrangements; e.g., butyric acids, leucine and isoleucine, glucose and fructose. ... (05 Mar 2000) ... 
Type: Term Definitions: 1. isomerism involving the same atoms in different arrangements, the butyric acids, leucine and isoleucine, glucose and fructose.
These are molecules with the same molecular formula but with different structural arrangements of atoms. See also: Isometry, Stereoisomerism.