Tetrazoles as Carboxylic Acid Analogs 147 



75% methanol when a rough comparison is made with the values for 

 other compounds determined in 50^ methanol. 



The data in Table 2 indicate that introduction of the electronegative 

 chlorine or bromine atoms as substituents on the benzene ring of 

 5-phenyltetrazole increases the apparent dissociation constant as com- 

 pared with the parent compound, whereas introduction of the electro- 

 positive methyl group decreases the apparent dissociation constant. 

 This might be anticipated from the inductive effects associated with 

 these substituent groups. However, from this point of view alone the 

 decrease in apparent dissociation constant observed for the methoxyl- 

 substituted compounds is not compatible with the slightly electronega- 

 tive character of this group. Ordinarily the position of a substituent 

 group should influence the extent to which its inductive effect is 

 transmitted by the benzene ring; the greatest effect upon apparent 

 dissociation constant might be expected when the substituent is nearest 

 the point of attachment of the carboxyl group. On this basis electro- 

 negative substituents should cause the apparent dissociation constants 

 to decrease in the order ortho > meta > para; the opposite order might 

 be anticipated for electropositive substituents. Since the observed 

 order of dissociation constants for the 5-aryltetrazoles is meta > 

 ortho > para, it is likely that factors other than inductive or field 

 effects are also influencing the magnitude of the dissociation constants. 

 A combination of the resonance concept and the inductive or field 

 effects of substituent groups will serve to explain the greater strength 

 as acids of the meta isomers as compared with the ortho and para 

 isomers. If we consider the 5-tolyltetrazoles first, the methyl group 

 may be assumed to exert its normal inductive effect which should cause 

 the 5-tolyltetrazoles to be weaker acids than 5-phenyltetrazole. 

 Furthermore, the electropositive methyl group would favor the forma- 

 tion of a field of relatively high electron density around the carbon 

 atom to which it is attached (scheme VIII). Such a field of high 

 electron density in the ortho or para positions would oppose the devel- 

 opment of a formal negative charge at these points and, in effect, 

 reduce the contribution to the resonance hybrid of forms involving 

 negative charges at these points. With the methyl group in the meta 

 position, although the inductive effect is in the same direction, an 

 increase in electron density at this point would offer less opposition 

 to resonance phenomena involving formal ortho or para negative 

 charges. Such an explanation is in accord with the observation that 

 both o-tolyl- and p-tolyltetrazole are weaker acids than ///-tolyltetra- 

 zole. Since resonance effects involving the benzene ring are not com- 



