Isomerism of maleic and fumaric acids

Isomerism of Maleic and Fumaric Acids.—The isomerism of maleic and fumaric acids is stereo-isomerism of the geometric type. It is exactly like that of the two crotonic acids (p. 177). 

The conception of electromerism involves the isomerism of maleic and fumaric acids, and in fact all isomerism heretofore classed under cis-trans or geometrical isomerism, without considering spatial relationships at all. Another group of substances may also be included under electromerism. Werner has placed in parallel the so-called... 

The interesting isomers are the ones that arise by replacement of H s on the different carbon atoms. One isomer is called cis ( on the same side, in Latin), where the two CTs are on the same side of the double bond. The other is called trans ( beyond one another, in Latin), where the two CTs are on opposite sides of the double bond. Since there is no free rotation around the double bond, cis and trans isomers coexist and are stable molecules having different properties (refer to Section 7.1 about van t Hoff and the isomerism of maleic and fumaric acids). 

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