HENDERSON. — CONCERNING POSITION ISOMERISM. C47 



the four valence energies of the central carbon atom will be equal, in 

 the compound CIl'lV's three will be e(iual and one different from these 

 three, and in the compound CR'R"R"'R"" all four will be different, even 

 when the central carbon atom is tied to like atoms by all four of its 

 valences as in methylethylacetacetic ester 



CH3\ /CO — CH3 



C,Ur/ \CO-O-C2H6 



because every one of the four carbon atoms which are tied to the cen- 

 tral carbon atom is different in position from every other and conse- 

 quently subjected to different influences from at least some of the 

 atoms of the molecule. 



It cannot be too strongly emphasized that this conclusion is a logi- 

 cal deduction from established experimental data with the aid of but 

 two postulates, the current theory of chemical constitution and the 

 current theory that the interatomic forces within the molecule are 

 exclusively (or almost exclusively) valence energies. 



It remains to be pointed out that through the consideration of 

 many cases similar to those here studied, one may hope to obtain 

 accurate quantitative information regarding the phenomena of orien- 

 tation of substituting groups ^"^ and the countless other cases familiar to 

 every organic chemist of the influencing of reaction by substituted 

 groups, and thus to replace the existing empirical rules for such cases 

 by accurately formulated principles. 



Summary. 



In development of the conception of varying valence energy it is 

 shown that the effect of an inactive atom group upon a reaction of 

 another atom group of the same molecule, measured by the heat of 

 reaction, varies in a regular way according to the relative positions 

 of the two groups. 



Curves are presented representing the nature of this variation in 

 one case of special importance because of the magnitude of the effect 

 and the accuracy of the data, and in a case where the effect is slight. 



It is shown that, in accordance with this conclusion and the previous 

 considerations, the valence energies of two ties between like atoms are 

 under like conditions equal, under unlike conditions different. 



The importance of these considerations for the understanding of the 

 influencing of reactions by substituted groups is pointed out. 



" Sec for instance Flurscheim, 1. c. 



