( 722 ) 



With this I consider the identity of these hydro-products and the 

 geometrical isomerism of the terpenes as proved. The isomer of 

 ocimene 1 will call in future allo-ocimene. It is remarkable that 

 allo-ocimene deviates 6,31 from the theory of Brühl; its index of 

 refraction is also greater than that of the hydrocarbon and it has 

 also a strong dispersion power. This, as Brühl thinks ^), is perhaps 

 connected with the presence of a conjugate system of double links. 

 Provisionally, one should be careful in drawing conclusions as other 

 substances also exhibit such differences. Allo-ocimene is, however, 

 in this respect a unicum in organic chemistry. Dihydro-ocimene on 

 the other hand exhibits the correct refraction. The deduced geo- 

 metrically isomerism was also veiy much supported by the behaviour 

 of the isomer towards a mixture of sulphuric and glacial acetic acid. 

 AVhilst ocimene remains for the greater pai't unchanged and is, to 

 a small extent, converted into an alcohol, allo-ocimene is for the 

 greater part converted into a polymerisation product, whilst there 

 is left a small quantity of terpene, which proved to be nothing else 

 but ocimene. This typical difference between the two ocimenes is 

 perhaps connected with the particular tension which the ethylene 

 link may attain here. Possibly, at the moment this ethylene link 

 opens, the two connected atoms of three molecules combine to form 

 a cycle of six atoms; a substituted hexa-hydrobenzene derivative 

 -would then be formed; the polymerisation product would be this 

 -triterpene. 



The regeneration of ocimene from allo-ocimene under the influence 

 of dilute acids renders the analogy complete with tiie isomerism of 

 fumaric and maleïnic acid. After what has been said, it is no longer 

 doubtful, that ocimene, which possesses the double link 5, is repre- 

 sented by formula I, whilst myrcene is represented by formula II, 

 which has now been deduced independently of the results of the 

 oxidation. But few instances of geometrical isomerism have been 

 noticed with hydrocarbons and this is the first known in the terpene 

 series. It seems to me not impossible that the absence of the cyclic 

 link has given nature the opportunity of forming a labile geometrical 

 •isomer ; it is remarkable, however, that this has taken place without 

 any admixture of allo-ocimene. I hesitate to pronounce just now an 

 opinion as. to the nature of that geometrical isomerism with ocimene 

 and allo-ocimene ; the following projection formulae seem to me the 

 most probable. 



2) Ber. 38, 761 (1905). 



