230 PHENOMENA, ATOMS, AND MOLECULES 



in the surface forces due to effects transmitted from atom to atom in the 

 molecule, by considering the chlorine-substituted fatty acids. In table 2 the 



TABLE II 



Dissociation Constants of Chlorine-substituted Fatty Acids 



Acetic acid 



Chloroacetic 



Dichloroacetic. . . . 

 Trichloroacetic . 



Propionic acid. . . 

 a-Chloropropionic 

 i3-Chloropropionic 



Butyric acid 



a-Chlorobutyric. . 

 (i-Chlorobutyric. . 

 Y Chlorobutyric. . . 



K 



1.85 X 10-= 

 155.0 

 5000.0 

 20000.0 



1.4 X 10-^ 

 147.0 

 8.6 



1.5 X 

 139.0 

 8.9 

 3.0 



10- 



Inr 



[0] 



+ 4-44 



7.6 



9.3 



[-0.26] 

 4.36 

 1.53 



[0.21] 

 4.30 

 1.57 

 0.48 



volts 







0.1053 

 0.190 

 0.233 



0.006 



0.1045 



0.0382 



0.0053 

 0.1038 

 0.0392 

 0.012 



values of the dissociation constant K for some of these acids are given as 

 taken from Landolt-Bornstein tables. In the third column, under the head- 

 ing In r, is given the natural logarithm of the ratio of K for the acid in 

 question to the value of K for normal acetic acid. According to the Boltz- 

 mann ecjuation, this quantity should be equal to "k/kT, where A represents 

 the difference between the work necessary to remove a hydrogen ion from 

 the given acid molecule and from an acetic acid molecule. Since kT is 

 equivalent to 0.025 volt, we can obtain the value of X in volts by multiplying 

 the values of In r by 0.025 ; the last column of the table gives these values. 



Comparing the monochloro acids with each other, we see that all three 

 of the acids in which the chlorine is in the a-position give A. = 0.105 'vo\t. 

 The two acids with chlorine in the /5-position give X = 0.039 "^o^t. The 

 single y-chloro acid for which data are available gives X = 0.012 volt. 



From theoretical considerations we should expect that any state of 

 strain which is transmitted from atom to atom along a hydrocarbon chain 

 should decrease exponentially as the distance increases. The above data 

 thus leads to the conclusion that the electric polarization produced by the 

 presence of a chlorine atom in a hydrocarbon chain decreases in the ratio 

 2.7 : 1 in being transmitted from one carbon atom to the next. If instead of 

 chlorine we should substitute other radicals, we might obtain electric forces 

 of different magnitudes, but in any case we should expect this ratio 2.7 : i to 

 apply to the decrease in the force from atom to atom. A considerable effect 

 is thus transmitted from one atom to the next, but very little is transmitted 

 as far as the second or third atom. 



