ISOMERIC CHANGE 



237 



tration, the dotted lines indicating the two ways in which the 

 compound may dissociate. 



H 



O- 



O.NO:C 



C 8 H, 4 < 



N< 



CO 



O Na 



>C 8 H M 



OC 



The catalytic action of ammonia may be of the same nature 

 as that of the alkalis, depending on the formation of an 

 additive compound of nitrocamphor with its ammonium salt. 

 But in view of its weak basicity it is possible that free 

 ammonia is the active agent, as in the conversion of ammonium 

 cyanate into urea, and that it acts by forming a compound 



C S H 



/ 

 4 \ 



H 



^N< 



'O.NH 2 

 O. H 



CO 



of the same type as those referred to above in discussing the 

 catalytic action of water, alcohol, and acetic acid. 



D. Optical Inversion 



The racemisation or inversion of optically active compounds 

 forms a special case of isomeric change which differs from 

 those exemplified above only in two respects. Firstly, the 

 product of isomeric change is an optical isomeride, the 

 structure of which is precisely similar to that of the original 

 material, and differs from it only in the order in which the 

 groups are arranged around the asymmetric atom which is 

 usually present in such compounds. Secondly, as the isomerides 

 differ from one another only in the same way as an object 

 and its image in a mirror, or a right-handed and a left- 

 handed screw, they must be equally stable, and when a con- 

 dition of equilibrium is attained must be present in equal 

 quantities, giving rise to an optically inactive or " racemic " 

 mixture. The necessity of dealing specially with this class of 

 isomeric changes arises from the widespread — but completely 

 unjustified — belief that the rearrangement of the groups can 

 be accomplished by merely shaking up the molecule without 



