ISOMERIC CHANGE 225 



CH 3 CH, CH 3 CH 3 CH 3 CH 3 



\s \y \/ 



C C CH 



I II I 



CH C CH 



H,C CH 2 H,C CH 2 HC CH 2 



II. II II 



HC CH 2 HC CH 2 HC CH 2 



V ^/ %/ 



C C C 



I I I 



CH 3 CH 3 CH 8 



Limonene Terpinolene Terpinene 



whilst the technical preparation of camphor from turpentine 

 may be quoted as illustrating the changes in ring-system that 

 may be effected by similar agents. The extraordinary fertility 

 of the process when applied to camphor itself has been dis- 

 cussed by Armstrong and Lowry, 1 and need not now be referred 

 to in detail. 



One other change depending on dissociation possesses great 

 historical interest — namely, the conversion of ammonium cyanate 

 into urea. There can be little doubt that in this case the 

 ammonium salt dissociates into ammonia and cyanic acid, and 

 that the change into urea depends on the recombination of the 

 ammonia with the cyanic acid functioning, not as an acid, but 

 as an isocyanate — 



C. Isomeric Changes of the Second Group 



(a) Transference of a Mobile Hydrogen Atom. — In striking 

 contrast to the isomeric changes of the first group, which involve 

 the interchange with a hydrogen atom of a halogen or of a 

 sulphonic, nitro- or hydroxyl group, is the behaviour of com- 

 pounds such as nitrocamphor which contain a " mobile " hydrogen 

 atom and undergo change with extraordinary facility. So far 

 as the mere formulation of these compounds is concerned there 

 is no great contrast between their isomerism and that of the 

 olefines, since in each case isomeric change involves only 

 the transference of a single hydrogen atom and the rearrange- 

 ment of the bonds in the molecule. The wide difference between 



1 "The Optical Inversion of Camphor and the Mechanism of Sulphonation," 

 Trans. Chem. Soc. 1902, 81, 1469. 



15 



