ISOMERIC CHANGE 245 



E. Velocity of Isomeric Change 

 Although, as has been shown above, every isomeric change 

 takes place in a complex molecular circuit, it is nevertheless a 

 fact that almost all the changes that have been studied obey the 

 " unimolecular law," which expresses in mathematical form the 

 fact that the rate of change at any particular moment is pro- 

 portional to the amount of material which awaits transformation. 

 The progress of the action can therefore be expressed by curves 

 and formulae of the simplest logarithmic type. It is necessary 

 to point out, however, that this simplicity of mathematical form 

 implies nothing more than that the catalyst, whether present in 

 minute traces or in such large excess as to play the part of 

 solvent, remains constant in quantity and in efficiency during 

 the progress of the action, and that if the transformation takes 

 place in successive stages these differ so widely in velocity that 

 the course of the action is controlled almost entirely by the 

 slowest of the processes. 



The unimolecular law has been established for the inter- 

 conversion of the two hexachloroketocyclopentenes l 



CC1=CC1\ CCl.CCl t \ 



i >co 11 >co 



CCU.CClo/ CC1.CC1/ 



for the conversion of phenylchloroacetamide into />-chloroacet- 

 anilide, 2 for glucose and a large number of other sugars which 

 undergo isomeric change — accompanied by a change of rotatory 

 power — in freshly prepared aqueous solutions, 3 for 7r-bromo- 

 nitrocamphor, 4 and for nitrocamphor itself 5 in several different 

 solvents and under a score of different conditions. It is indeed 

 altogether exceptional to find a case of isomeric change which 

 does not obey the unimolecular law, and it is to the exceptions 

 rather than to the multitude of regularities that interest specially 

 attaches. Two such exceptions may be referred to briefly. 



(a) Phenylchloroacetamide. — Orton has shown 6 that the con- 

 version of this compound into /-chloroacetanilide, 



C 6 H 5 . NCI . CO . CH 3 -> CI . C S H 4 . NH . CO . CH 3 



1 Kuster, Zeit.phys. Chem. 1895, 18, 171. 



2 Blanksma, Rec. Trav. Chim. 1903, 22, 290. 



3 For a list of these sugars, see Trans. Chem. Soc. 1899, 75, 214. See, for 

 example, Trey, Zeit.phys. Chem. 1895, 18, 198 ; Osaka, ibid. 1900, 35, 66. 



4 Lowry, Trans. Chem. Soc. 1899, 75, 227. 



5 Lowry and Magson, Trans. Chem. Soc. 1908, 93, 109. 



6 British Assoc. Report, Winnipeg, 1909. 



