196 REPORT—1904. 
Physical Phenomena explained by Butlerow’s Theory.—In addition to 
affording an explanation of many puzzling chemical changes the theory of 
dynamic isomerism has proved exceptionally fertile when applied to 
physical phenomena. Thus the gradual change of rotatory power which 
takes place in freshly prepared solutions of many of the sugars was 
observed as long ago as 1846 but has only recently been shown to be due 
to the establishment of equilibrium between isomeric forms of the sugar. 
The formation of violet salts from colourless violuric acid, of red and 
yellow salts from colourless p-nitrophenol and of highly dextro-rotatory 
salts from levo-rotatory nitrocamphor are due to similar changes or 
structure. Again there is good reason to suppose that many of the 
phenomena of luminosity are dependent on reversible isomeric change or 
on the analogous reversible changes involved in association and dissociation. 
This is almost certainly true of the fluorescence and phosphorescence or 
organic compounds and there is reason to think that the flash of light 
emitted when crystals of sugar or saccharin are crushed is also a mani- 
festation of isomeric change.! 
The bearing of Dynamic Tsomerism on Chemical and Physiological 
Changes.—The mere presence of the mechanism necessary for dynamic 
isomerism appears to facilitate chemical change and in many cases it is 
probably an essential factor. Thus Lapworth has recently shown? that 
the bromination of acetone is dependent on the presence of a minute 
amount of the enolic form, the ketone itself being apparently unacted on 
by the halogen. A similar explanation may be given of the great activity 
of phenol and aniline as compared with benzene and of the inhibiting 
influence of ortho- substitution. In this connection it is of interest to note 
that the most important natural organic materials, such as the sugars 
and the albuminoids, are very rich in those plastic groups which most 
frequently give rise to dynamic isomerism and to this fact their great 
activity may at least in part be attributed. 
Il. The Natwre of Dynamic Isomerism. 
1. Definition. Under the heading of dynamic isomerism are included 
all those cases in which it is possible to establish a condition of equilibrium 
between isomers. It may also be defined as a condition of reversible 
isomeric change.? But if this definition is used it must be remembered that 
reversal is largely a matter of conditions and that all isomeric changes 
are probably accompanied by a certain amount of back-action, even though 
this may be too small to be detected by the methods commonly used. 
2. Equilibrium between Isomers is only possible in presence of a 
third substance.—Proof of this was first obtained in the case of nitro- 
camphor,‘ solutions of which in chloroform could sometimes be kept for 
two or three weeks without undergoing change, although usually sufficient 
impurity was present in the solution to bring about equilibrium between 
the normal and pseudo forms in the course of a single week. 
CH.NO C: NO.H 
STEN ay Re: Be ae rg > Cae * [18 0 
[82 %] 10 M\ co s 10 do [ %] 
Normal nitrocamphor Pseudo-nitrocamphor 
1 Armstrong and Lowry, Proc. Roy. Soc. 1903, 72, 258. 
= Trans. Chem. Soc. 1904, 85, 30. 3 Lowry, Trans. 1899, 75, 235. 
+ Lowry, ibid, p. 220. 
