MUTUAL INFLUENCE OF GROUPS 



101 



The values of K thus measured are suitable for judging 

 of the influence we are considering, not only on account of 

 the facility of determination, but because they vary so 

 greatly amongst themselves. Thus the influence of chlorine 

 at 25 in strengthening an acid is shown by the numbers : 



Acetic acid, CH 3 COOH iooK= 0-0018 



Monochloracetic acid, CH 2 C1COOH ... = 0-152 



Dichloracetic acid, CHC1 2 COOH .... 5-14 



Trichloracetic acid, CC1 3 COOH .... =121 



and in crotonic and isocrotonic acids, isomers of the formula 

 CH 3 CHCHCOOH, chlorine shows, as might be expected, 

 a greater influence on K when near than when far from the 

 carboxyl ; the numbers again refer to 25 : 



a Chlorderivative (CH 3 CHCC1COOH 

 & (CH 3 CC1CHCOOH 



Crotonic acid 



0-00204 



0-072 



0-0144 



Isocrotonic acid 

 o 0036 

 0-158 

 00095 



Since we have here an indication of the possibility of 

 determining relative distances within the molecule, we 

 must mention the qualifications so far existing. 



On the theoretical side it must be remembered that, in 

 consequence of the unequal distribution of matter in the 

 molecule, an action is rarely propagated equally in all 

 directions within it. 



On the experimental side it appears that sometimes 

 a group in the meta-, sometimes one in the para-position 

 behaves as if it were at the smaller distance. This is 

 shown in the following ortho- (1.2), meta- (1.3), and para- 

 (1.4) derivatives in the benzene series 1 . 



1 Loewenherz, Zeitschr.f. Phys. Chem. 25. 385. 



