128 



Professor Julius Wilhelm Brilhl 



[May 26, 



The withdrawal of these two atoms and the closing of the ring have 

 therefore taken place without causing any optical anomaly. 



In the formation of the olefines and diolefines from the paraffins, 

 however, there is no closing of the ring. These substances are of 

 open-chain structure, and every removal of 2 hydrogen atoms corre- 

 sponds here to the creation of a double carbon bond : — 



H3C • CH.- CH,- CH2- CH,- CH3 CHjZCH • CHj- CHo' CH.* CH3 



Hexane Hexylene 



CHo =CH • CH,- CHj- CH Z CHg 

 Diallyl 

 (CeH.o) 



Hence, also, the refractive increment of the olefines and diolefines 

 is directly proportional to the number of hydrogen atoms removed 

 from the paraffin. 



From all this it follows that the removal of hydrogen atoms 

 causes optical anomalies only where double carbon bonds are created 

 by the process. The splitting-off of hydrogen tvhich results in a closi?ig 

 of the ring is, on the other hand, without abnormal optical influence, and 

 inoduces no refractive increment. 



This latter principle, which has since been confirmed many times 

 by experiment, has proved of the same importance as the first in the 

 investigation of the chemical structure of bodies. 



§ 14. A few examples will show how these two principles can be 

 utilised for the discovery of chemical structure. 



Besides the formula already mentioned for benzene — that suggested 

 by Kekule — several others have been proposed, e.g. those by Ladenburg 

 and Claus : — 



HC 



HC 



CH 



CH 



HC 



(Ladenburg) 



(Claus) 



Neither of these graphic formulae is reconcilable with the results 

 of spectro-chemical investigation, because the neighbouring carbon 

 atoms contained in them are associated only by single cycloid or 

 ring-closing affinities, and not by any so-called double bonds. Sub- 

 stances of this kind should be optically normal, while benzene and 

 its derivatives are as a matter of fact abnormal. Kekule's formula 



