io Lapworth, Latent Polarities of Atoms 



may be made to the three isomeric cresols. In these the 

 influence of the hydroxy lie oxygen as " key-atom " on the 

 hydrogen atoms of the methyl group will evidently be such, 

 if anything, as to increase their " positiveness " in the homo- 

 geneous m-cresol and to depress it in the heterogeneous p- 

 and 0-cresols. The influence of the methylic hydrogens, 

 acting as " key-atoms," on the hydroxy lie group, is as 

 indicated in the generalised scheme — 



OHW 



+ 

 The enhanced degree of polarisation, — O — H, in the 

 hydroxyl groups of the homogeneous m-cresol contrasted 

 with the opposite effect in the other two isomers, indicates that 

 m-cresol is the most acidic of the three; in o-cresol the 

 proximity of the -OH group to the "key-atoms" suggests 

 that in this compound their depressant influence will be more 

 marked than in ^-cresol. This arrangement, m-, p-, and 

 o-cresol, in descending order of acidity, is precisely what is 

 found to hold good. (Dawson and Mountford, Trans. Chem. 

 Soc, 1918, 113, 987.) 



Comparison of the cresols with phenol is not admissible, as 

 the general basylous effect of methyl as compared with 

 hydrogen would have to be taken into consideration, just as, 

 for example, would have to be done in comparing acetic acid 

 with formic acid ; in both cases methyl depresses the acidity. 

 Whilst the principle of induced alternate polarities serves 

 to group together a large number of otherwise apparently 

 disconnected data, it is likely to remain comparatively infertile 

 unless considered in conjunction with more purely chemical 

 features, and especially with the question of free, partial and 

 latent valencies and their interactions of which conjugation 

 may be specified as a type. 



