1*83 



Opposed to this stands tlie view of Hiilmann ') that the differences 

 of the (illoacids must l)e attribuled to triniorphism whereas Rhber 

 and GoLDsciiMiDT ^) consider the occurrence of' <;- and (J-Storax cinna- 

 mic acid as a typical case of dimor|)hisni. 



The changes which (c- and |?-Storax cinnaniic acid suffer in sun- 

 light afford us a view on tiie difference existing between those acids 

 in the solid condition. The polvnierisatiun jiroducts of these acids 

 are, as we noticed, ti- and i:f-lruxillic acid to wiiich are attributed 

 the following formulae as being the most likely : 



«-truxillic acid i^-truxillic acid 



C„H, — CH -- CH - COOH C,,1I, — UH — CH — COUH 



HOOC ~ CH — CH — C„H, ( '„H, — CH — CH — COOH 



As to the i)osition of the gi'oiips with regard to the |)lane of the 

 4-ring not much is known ; in the case of ,:?-truxillic acid the proba- 

 bility is that the COOH groups are found at the same side. 



From these structural formnlae it is plainly perceptible that one 

 molecule of these truxillic acids is generated from two molecules of 

 cinnaniic acid anti liial tlie dilferent manner in which the comliination 

 takes place gi\cs rise to the occurrence of two truxillic acids. 



Hence it must be assume<l thai there exists between <;- and ,-?- 

 truxillic acid such a dilfeienre dial the first, by the action of 

 light, renders possible only a bond sucli as occurs in «-truxillic acid, 

 whereas the /?-Storax cinnaniic acid must be such that only the 

 binding as present in iJ-truxillic acid can take place exclusively. 



A dilferenl placing of the groups in the molecule in regard to 

 each other, which Eui.KNMi'iYiat suggests lo explain the difference 

 between a- and ii- cinnaniic acid carmot avail us tis even then for 

 each formula the linking of two molecules can always take place 

 in such a manner that both a- and ,?-truxillic acid can form. 



If, however, we assume that the position of the molecules in the 

 crystals is different for the two acids, a different bond due to the 

 action of light might be coupled with this. The different behaviour 

 of the acids might then be looked for in a different arrangement 

 of the molecules in the "Kaumgitler". 



The following hypothesis may also be proposed. As is well known '), 

 most probably all organic acids dissolved in hydroxyl-free solvents 

 possess double molecules. Hence there is a great probability that in 



1) I'er. 42, 184 (1909). Ber. 43, 5Ü9 (1910). 



2) tier. 43. 461 (1910). 



') Van 't Hoff. Vorlesuiigcn iiber theoretische unci physikalische Chcuiie, zweites 

 Heft, pg. 52. 



13* 



