THE CHEMICAL HISTORY OF THE TERPENES 61 



where two molecules of isoprene are united by the dotted lines, 

 the valencies adjusting themselves but without further change : 



CH.CMe:CH 2 



ch/'s.ch, 



CH^/CH 



CMe 



To represent the condensation of isoprene into caoutchouc, 

 Harries l assumes the formation of an octadiene as the first 

 product of the union of two molecules of isoprene, rubber 

 consisting of multiples of this or (C 10 H 16 ) n . 



CMe CMe 



CH, CH CH CH 2 



II I I 



CH, CH, CH 2 CH 2 



II I I 



CH CH 2 CH 2 CH 



CMe CMe 



Caoutchouc is a colloid of very high molecular weight and 

 if it is assumed to be made up of a number of such groups 

 united together, it is difficult to explain why rubber should 

 break down so easily in groups of C 5 H 8 and why its combining 

 capacity is represented by four atoms of bromine for every ten 

 atoms of carbon. 



Thiele's theory of partial valencies has been invoked by way 

 of explanation but this is itself a subject of extremely doubtful 

 character. 



Other formulae have been suggested but the whole question 

 is one which requires much further investigation. 



Finally, it may be remarked that the terpenes and their 

 derivatives afford many examples of optically active compounds 

 which, however, do not owe their activity to the presence of 

 one or more asymmetric carbon atoms but rather to the 

 asymmetry of the molecule as a whole. This phenomenon, 

 however, is not peculiar to the terpenes and the question is too 

 large for discussion on this occasion. 



1 Berichte [1905], 38, 3985. 



