ISOMERISM

(chem.), is the phenomenon seen when compounds occur having the same molecular formula but different constitutions. Such compounds are called Isomers or I some rides, and they differ in the arrangement of their atoms. For every po ible arrangement of atoms with a given valency, there is a Graphic Formula representing an isomer. Thus supposing carbon to be tetravalent, the hydrocarbon butane with the molecular formula C4, Hio, can be represented by two graphic for mule. There should be and there are two isomers. The number of po ible isomers increases with the number of carbon atoms in the molecule —Optical, Physical, or Stereo-Isomerism: these isomers have the same graphic formula, but they differ in their action on polarised light and in certain physical properties. Such isomerism occurs only in substances which have a carbon atom combined directly with four different groups (asymmetric carbon atom).