301 Professor William J. Pope [May 1, 



remarkable rigidity with which the atoms are held together in the 

 molecule ; it might therefore be anticipated that by actually making 

 all the isomerides having the constitution indicated above, some 

 means would be aflforded of judging whether the van't Hoff-Le Bel 



Q, ,0 



^~0 



Fig. 1. 



or the Kekule view forms the closest approximation to the truth. 

 Kekule's constitutional formulae indicate the existence of two isomeric 

 compounds of the following types — 



OH CH3 



CH3— C— COoH and HO— C— CO^H 



I ' \, ' 



whilst, on the van't Hoff-Le Bel view, two isomerides should exist 

 in which the four groups, H, CH3, OH, and COoH, are arranged about 

 the central carbon atom in the manner indicated in Figs. 3 and 4. 



Although in each case two isomerides would be obtained, the 

 examination of the two kinds of figure reveals very essential differ- 

 ences. The solid figure isomerides differ only in that the one is the 

 image in a mirror of the other — they are related in the same kind of 



way as a right- and a left-hand glove. The differences observable 

 between two molecules thus related should consequently not be differ- 

 ences of an ordinary chemical nature, but differences involving 

 merely a kind of chemical, physical and mechanical right- and left- 

 handcdness. The Kekule constitutional formula3, on the other hand, 

 would indicate — if they indicate anything — that the substances to 

 which they refer differ in the more gross way in which ordinary 



