34 THE ROYAL SOCIETY OF CANADA 



or hydrochloric acid. That bromine and hydrochloric acid add to a 

 polymerized compound like rubber constitutes no proof that ethylene 

 linkages are present in the original rubber molecule. 



(4) Ditmar (22) has produced a dinitro compound by the action 

 of nitric acid in rubber. This was verified by Harries. Ditmar has 

 shown that this compound is a dinitro cumic acid of the constitution 



A 



CHz C-NO2 



CHp C-NO2 



C'QH 



This contains a six membered ring and closely resembles di- 

 pentene. Its formation from a molecule containing dipentene as a 

 constituent part could be easily understood. Its formation from a 

 mol containing only dimethyl cyclo octadiene is not capable of any 

 easy explanation. 



(5) The synthetic rubbers made by Harries from butadiene, 

 methyl butadiene (isoprene) and dimethyl butadiene by polymeriza- 

 tion with metallic sodium, and which Harries believes possess the 

 cyclo octadiene structure, are much more easily oxidized than natural 

 occurring rubber. These synthetic rubbers possibly consist solely of 

 octadiene constituents and as a consequence contain ethylene linkages 

 which thus render these synthetic rubbers more susceptible to the 

 action of oxygen, the greater stability of the natural rubber being due 

 to the absence of such unsaturated bonds. 



A New Constitution for Rubber. 



For these reasons a provisional working hypothesis was set up 

 that the rubber molecule contains within it a dimethyl cyclo octadiene 

 part, a dipentene part and an isoprene part. 



The various probable methods of polymerization of ^ isoprene 

 were then examined. It is obvious that isoprene can polymerize in 

 two ways: 



(1) By means of the free bonds, thus 



