ON DYNAMIC ISOMERISM. 195 
Abnormal Chemical Changes explained by Butlerow’s Theory.—Simul- 
taneously with the development of the theory of dynamic isomerism a 
large number of observations were being made which have only found a 
satisfactory explanation in the fully developed theory. The formation 
of two series of ethers from prussic acid was explained by Butlerow 
in 1877. Baeyer in 1883 was able in a similar manner to account for 
CO CO 
aa EN PAGER 
the existence of isomeric ethers C,H, CO and C,H, C.OEt 
os 
NEt 
of isatin by supposing that one of them was derived from a labile pseudo- 
isatin which was converted into ordinary isatin whenever attempts were 
made to prepare it :— 
co co 
A \ 
C,H, CO or C,H, CoH 
EY Oa oc 4 
NH N 
In the same way it is easy to account for the apparent identity of nitroso- 
phenol and quinoneoxime by supposing that one of these compounds 
undergoes isomeric change in the course of preparation : 
_> 
ON.C,H,OH or HON: 0,H,: 0. 
<_—— 
Laar’s Theory.—In his paper, ‘ Ueber die Méglichkeit mehrerer Struk- 
turformeln fiir dasselbe chemische Verbindung,’ Laar, in 1885, rendered 
an important service by calling attention to the existence of a large 
number of facts of this kind. Unfortunately he rejected the explanation 
given above and put forward in its place his theory of tautomerism. 
According to this theory the product obtained by the action of nitrous 
acid on phenol, or of hydroxylamine on quinone, has actually not one but 
both of the alternative constitutions formulated above, the hydrogen atom 
oscillating between the two positions indicated in the formula 
CH CH 
cH cH CN iy 
7O0C 
POET O19 VE OY 
in a manner comparable with the vibrations that give rise to light. The 
incorrectness of Laar’s theory was proved when, in 1895 and the years 
immediately following, it was found that the isomeric forms of several 
ketones and nitro- compounds could be isolated in the solid state and were 
only slowly converted into one another. The necessity for a catalytic 
agent has also shown that the oscillation of the hydrogen atom is not an 
intramolecular process but, like other chemical changes, can only take 
place within a complex molecular circuit. The distinction between the 
two theories is of importance at the present time, because it is not 
inconceivable that tautomerism may actually exist as an intramolecular 
phenomenon, though all the cases to which the term has hitherto been 
applied:appear to be examples of dynamic isomerism. 
02 
