CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



CONCERNING POSITION ISOMERISM AND HEATS 



OF COMBUSTION. 



By Lawrence J. Henderson. 



Presented by T. W. Richards, January 9, 1907. Received December 20, 1906. 



Current ideas of valence consist of two distinct conceptions, quan- 

 tivalence and valence energy, which rest upon two bodies of fact of 

 different sorts. Of these conceptions quantivalence has played by far 

 the greater role in the development of organic chemistry and of stereo- 

 chemistry, though the consideration of valence energy is present or im- 

 plied in Le Bel's discussion of the asymmetric carbon atom, in von 

 Baeyer's "Spannungstheorie," in Thiele's theory of partial valence, 

 and in Werner's stereochemical theories and recent publications. In 

 Richards's recent discussions of the compressible atom the conception 

 of valence energy has shown itself more pertinent than the conception 

 of quantivalence, and in the theoretical discussion of thermochemical 

 data it has been, and of course is, of the greatest moment. 



Conclusions regarding valence energy which are based upon heats of 

 combustion are open to the criticism that from measures of the magni- 

 tude of the total-energy change it is sought to determine the magnitude 

 of a quantity which depends perhaps entirely upon the free-energy 

 change. Yet even to-day the determination of heats of combustion 

 remains the one way possible of gaining quantitative data regard- 

 ing the magnitude of valence energy in organic compounds, and it is 

 probable that such information, properly interpreted, leads to not 

 inaccurate conclusions. On the contrary, these conclusions may be 

 very accurate when differences between the heats of combustion 

 of similar substances are considered, and when such differences in 

 very similar cases are compared, as in this paper, there is good rea- 

 son to believe that changes in bound energy have been almost wholly 

 eliminated. 



Of these two ideas concerning valence, that of valence energy is the 

 less clearly defined. J. Thomsen, it is true, has sought to show that 



