UNSATURATED Acids Isocrotonic Acid

CIS-a,/ -UNSATURATED ACIDS ISOCROTONIC ACID [(-Z)-Crotonic acid]... 

ISOCROTONIC ACID, 53,123 a,p-Unsaturated carbonyl compoimds, preparative method, 50,70... 

The interest in these compounds centers in crotonic acid, as an acid is known, isomeric with crotonic acid, which differs markedly from it in physical properties, but appears to have, as a result of the study of its chemical properties, a structure which is best represented by that given to crotonic acid. As the three formulas given above are the only ones possible for acids containing a double bond and having the composition C3H5.COOH, and as four well characterized substances of this composition are known which show the kind of unsaturation represented graphically by the so-called doubly-linked carbon atoms, an extension of the structure theory as developed so far is necessary. Isomerism similar to that shown by crotonic and isocrotonic acids, has been observed in many compounds which contain double bonds. 

The presence of a double bond in the unsaturated acids leads to an opprountiy for isomerism like that shown by crotonic and isocrotonic acids (127). The two forms in the case of the dicarboxyl derivatives of ethylene are represented by the formulas —... 

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