85 



chemical methods that can serve (o determine the conligiiratioii, we 

 will demonstrate that here too there is a way out. 



It is evident that, if less characteristic radicles are l)onnd to the 

 nucleus, as in the cyclohexanediols 1-4 or the hexahydro-toluilic 

 acids, with which no discernment by resolution into optical antipodes 

 is feasible, it seems impossible to determine the configuration. 



Here the difference which appears in the formation of complex 

 compounds, for instance of the diols with boric acid, has proved 

 promising; this has been evidenced by the configuration determination 

 of some sugars, but on that point we will not expatiate here. 



3. Secondly the configuration may be deduced from what happens 

 if the double bond is saturated; the so formed compounds are diffe- 

 rent as they originate from the cis or from the ti-ans isomer. 



The configuration may also be inferred from the way of formation, 

 eithei' from saturated compounds by elimination of parts of the 

 molecule, or from acetylene derivatives by partial saturation, or by 

 substitution of groups it) compounds, of which the configuration 

 is known. 



The last mentioned modes of determination, by which the bonds 

 between the atoms are vigorously attacked, have often caused con- 

 fusion, by which their trustworthiness has been impaired. When 

 applied to fu marie and maleic acid, they at first seemed to answer 

 excellently; we can still assert with satisfaction that fumaric acid 

 is changed by KMnO^ into racemic acid and maleic acid into ineèto- 

 tartaric acid. 



Only, the brilliant researches of Wislicknus about the bromination 

 of both acids, followed by elimination of one molecule of HBr, by 

 which fumaric acid furnishes first racemic dibromo-succinic acid and 

 then bromo-maleic acid, and maleic acid first meso (/;y6>-)dibromo- 

 succinic acid and then bromo-fumaric acid, have turned out to be 

 correct only as far as the final products are concerned. 



McKenzie ^) and Bkor Holmberg -) namely have demonstrated 

 that wö-dibromo-succinic acid with the lower m. p. can be resolved 

 into optical antipodes and this entirely overthrows the deduction. 



As well at the addition of bi'omine to both acids, as at the elimi- 

 nation of HBr, exactly the reverse occurs from what we could expect, 

 and this inversion appears to be rathei' common. 



By the action of PCIj on aceto-acetic acid two isomeric |?-chloro- 



1) Proc. Ghem. Soc. 1911, 150. 



2) Journ. pr. ch. 84 145 (1911). 



