452 SCIENCE PROGRESS. 



mainly with stereoisomerism ; it has concerned itself only 

 with such bodies as could be isolated in numbers un- 

 accounted for by any possible application of structural 

 formulae. In many cases the configuration attributed to 

 these bodies by the tetrahedron hypothesis has been con- 

 firmed by the study of their reactions. 



But we have now to consider cases in which the study 

 of reactions has been the first step, and has led to stereo- 

 chemical theories, such as have been developed more 

 especially by Bischoff under the title of "the dynamic 

 hypothesis ". This name, chosen because the object of 

 these studies was to determine the motion of the atoms, as 

 well as their average position, seems appropriate also because 

 the subject of the investigations has been the reactions of 

 bodies, rather than the number of their isomers — chemical 

 dynamics rather than statics. 



The phenomenon of ring-formation has already afforded 

 a striking example of the connection between reactions and 

 the space relations of the atoms concerned. The formation 

 of a carbon ring has been seen to depend on the number 

 of its members, and on the relative position (cis- or trans-) 

 of the groups whose interaction closes the ring. But, as 

 Bischoff points out, the nature of the atoms connected with 

 members of the ring not directly concerned in the closing 

 thereof has also an effect. Thus a methyl group sub- 

 stituted for hydrogen in the system of succinic, of maleic, 

 or of glutaric acid facilitates the closing of the ring, — forma- 

 tion of an anhydride. In other cases, however, methyl 

 prevents or renders difficult the ring-formation. Some- 

 times, indeed, in a compound containing several methyl 

 groups it is easier to obtain a molecular re-arrangement than 

 a simple ring-formation. Thus instead of 



CH 3 



II. 



