( 721 ) 

 C C — C 



c = c c — c 



y > // > 



c c — c 



8 7 



which has already been agreed to by Semmler on other grounds. 

 Which of the abov'e formulae, however, belongs to ocimene and 

 which to myrcene? A choice is only possible on the strength of other 

 data. As has been stated, Semmler had assigned to myrcene for- 

 mula II on account of the formation of succinic acid in the oxida- 

 tion. Independently of him and these considerations, I had constructed 

 for ocimene formula I as the result of my oxidation experiments, 

 but without attaching any value to this. A closer consideration of 

 the above formulae, coupled with the peculiar behaviour of ocimene 

 on heating, as observed by va.n Romburgh, led me to the discovery 

 of a fact, which rendered a choice possible with great certainty. 



In one respect formula I differs characteristically from formula II 

 namely by the presence of the double link 5, which forms an 

 asymmetric system with the carbon atoms combined thereby and the 

 groups attached thereto, and so gives an opportunity for the existence 

 of a geometric isomerism. The transformation of ocimene into its 

 isomer led me to think that these two substances might be geome- 

 trically (stereo-) isomeric. Geometrical isomers are often readily con- 

 verted into each other on warming ; for instance, Wislicenls noticed the 

 transformation of the one bromobutylene into the other on distillation. 

 The hypothesis ad\anced by me was easy to verify for on hydro- 

 genation the same dihydro-ocimene ought to be formed from the 

 isomer as from the ocimene itself. This proved indeed to be the case. 

 The physical constants of these niaterials^were indeed identical as 

 is shown from I he following table : 



sp. gr.15 nd.jj b.p. at 761 mM. 



dihydro-ocimene 0,7792 1,4507 166°— 168° 



dihydro-isomere 0,7793 1,4516 167°— 168° 



whilst the original products exhibit strong ditferences as is shown 

 from the subjoined ') : 



sp. gr.,, nd. b.p. at 760 raM. 



ocimene 0,8031 1,4857 172°,5 



isomer 0,8133 1,5447 IBS'' 



') The constants of the isomer have been determined with the aid of a purer 

 preparation than those previously communicated. On heating ocimene some by- 

 products seem to be formed. 



