458 
CHEMISTRY: COM BERG AND SCHOEPFLE 
It is doubtful whether the matter is quite as simple as it is represented 
by the above equation. From a variety of experimental evidence^ 
the conclusion seems inevitable that both the hexa-arylethanes and the 
triarylmethyls exist in two tautomeric modifications. It is far more 
likely that triarylmethyls, at least when in solution, conform to the follow- 
ing scheme 
In other words, there is a tautomeric equilibrium between the benzen- 
oid hexa-arylethane (I) and the quinol (II); also between the benzen- 
oid triarylmethyl (III) wherein the central carbon atom is trivalent and 
its quinonoid modification (IV) wherein the />am-carbon atom in the 
nucleus assumes the trivalent state. This viewpoint is in entire harmony 
with the peculiar chemical and physical behavior of this class of com- 
pounds. It permits us to explain, by the presence of the quinol tautomer 
(II), the existence of a colored modification of hexa-arylethanes in cases 
where molecular weight determinations fail to indicate an actually 
measurable degree of dissociation. And even in those cases where a 
partial or complete dissociation of the hexa-arylethane is demonstrable, 
the fact that the solution is colored finds a more reasonable and more 
concordant explanation in the existence of the quinonoid tautomeric 
triarylmethyl (IV) than merely in that of the benzenoid (III) alone.^ 
Whether, however, the supplemental hypothesis of tautomerism is 
accepted or not, the fact remains that we are dealing primarily with a 
phenomenon where a hydrocarbon dissociates spontaneously into two 
parts, which parts may, also spontaneously, reassociate with the pro- 
duction of the original substance. What are the factors which influence 
the degree of dissociation in a given hexa-arylethane? What is the re- 
lation between the degree of the dissociation and the nature of the aryl 
group in the substituted ethane? 
Factors Influencing Dissociation. — Obviously, the nature of the solvent, 
the temperature of the solution, and the concentration of the solute 
must be the chief factors as regards the extent of dissociation which 
may be reached by a given hexa-arylethane. With regard to changes 
in the equiHbrium between the dimolecular and the monomolecular 
modification due to the temperature, it has been found^ that the mole- 
ular weight of triphenylmethyl in naphthalene at 79°-80° is approxi- 
mately 414, while the average value found with other solvents such 
(I) RsC CR^ 
11 
(II) R2C = < 
