HENDERSON. — CONCERNING POSITION ISOMERISM. 



64) 



-649 



In the presence of COOII — G56 



D'iffereyices from —645 Cal, the "normal" Value 



y 

 -646 



In the presence of COOH 



-11 



-4 



V 



-1 



It is apparent from a consideration of the above tables that the 

 effect upon the heat of reaction of a molecule exerted by a group which 

 is itself not directly concerned in the reaction varies in a regular way 

 with variation in the position of the group with respect to the react- 

 ing portion of the molecule. This is most clearly apparent in the 

 reaction CH3 — COOH in the presence of the group COOH, probably 



Cal 



170 



ICO 



150 



140 



a 



^ 



8 

 Curve I. 



because here the effect is great and the data abundant and accurate. 

 In this case, when the carboxyl group is a to the reacting group 

 the heat of reaction is diminished by 13 Cal., compared with its 

 "normal " value in the absence of the carboxyl group ; when the car- 

 boxyl group is in the /? position the heat of reaction is diminished by 

 about 3 Cal. ; when the carboxyl group is in the y, 8 or e position it is 

 increased by about 2..5 Cal., returning finally to the "normal" value 

 when the distance between the two groups is gi'eater. The effect 

 may be represented by the accompanying curve. -^^ 



^' The nature of this curve is apparently inconsistent witli the idea developed 

 by Fliirscheiin (I.e.) and by Biach (Zeits. f. physikalische Chemie, 50, 4;>, ICOJ) tliat 

 valence enerfry alternately increases and decreases from one carbon atom to the 

 next, in a chain or ring ; the period of alternation beintr, in the present matter, some- 

 times one carbon atom, sometimes more, according to the nature of the case. 



