268 



activity, seems to prove, that the presence of the optically active 

 phenyl-lactic acid has induced a definite stereometrical arrangement 

 in the molecule of the cinnamic acid, so that its configuration can 

 no longer be explained as a molecule with "double bonds" between 

 the unsaturated carbon-atoms, but as having two free affinities. 

 A similar "asymmetrical induction" seems to be also observed by 

 him and his collaborators in the presence of other optically active 

 molecules like d-, or l-tartric acids, etc. Cinnamic acid is, according 

 to his experience, only therefore usually optically wactive, because 

 it is a "racemic" compound of its two optical antipodes, which, 

 however, tend to change very easily into one another. 



In its molecules the two unsaturated carbon-atoms are situated 

 in a plane parallel to that of the four other substituents : C R H 5 , 

 C0 2 H, H, and H', or to that of three of them and one of the empty 

 places at the corner of the tetrahedra corresponding with each of 

 the unsaturated carbon-atoms ; in the last case, the four substituents 

 are evidently dispersed in space as situated in the corners of an 

 tVregular tetrahedron. According to Erlenmeyer, the six possible 

 forms of the different isomeric cinnamic acids hitherto observed, 

 might then possibly be represented schematically as follows: 



H 



COOH H' 



COOH 



COOH 



Storax-a-Cinnamic Acid. Storax-B-CinnamicAcid. TriclinicCinnamicAcid. 



acid is much more soluble in ether than an intentionally prepared mixture 

 of' inactive cinnamic acid -\- active phenyl-bromo-lactic acid with the same 

 rotation. 



Also from d-phenyl-bromo-lactic acid the mixed zinc-salt: 



C 6 H 5 CH(OH) CH 2 COO Zn COO CH = CH C Q H 5 

 was prepared by reduction with zinc and alcohol] although the calculated 

 rotation of this salt should be less than -\- 138', it showed, a rotation of 

 -f- 55', i. e. about four times the expected value; a deviation which in fact 

 can only be explained by the supposition of the cinnamic acid being activated. 

 From this salt an optically active cinnamic acid could finally be isolated, which 

 showed a specific rotation of -}- 148', and even hemihedral crystalform. 



