Theory of Molecular Volumes. 985 



self-same process. In practice only one (Form II.) would be 

 possible. As a matter of fact, only one ethylene di-substitution 

 product is known. 



On the plane we represent the change : — 



> 



X-CH 2 



I 

 ■CH,— X 



CH,- X 



1 !! 

 CH 2 - X 



Carbons Doubly Linked. 



When the carbons are doubly linked, rotation cannot occur 

 for the reason that this would take place against a resistance 

 offered by a field of force in the region between the two 

 C atoms. Thus the two isomers are more or less stable and 

 are indeed found. This is indicated by the well-known 

 diagrams : — 



X-CH 



CH-X 



Maleic form 



CH- 



II 



X 



ii 



ii 



n 



ii 





CH- 



X 





Fumaric 



for 



m 



The two forms according to our hypothesis would possess 

 different volumes and boiling-points. The fumaric modi- 

 fication would follow the Additive Rule, and the maleic 

 modification would be subject to a contraction. 



This is indeed the case if we are to judge by the densities 

 at ordinary temperatures. 



Maleic Ester. 

 Ethyl. 



OH-COO C 2 H 5 - 



Fumaric Ester. 



C, H 4 .CO O-CH 



CH - C C 2 IV 



d 20 (Knops)... 1-06917 



B.P 225° C. 



V E p (calc.).. 191-9 



CH-C U IU 



dw (Knops)... 1-05199 

 218° 0. 

 197-6 



-2-7 



