174 REPORT—1904. 
a—C—b 
(iii) Lsomerism in compounds of the type | 
—¢. 
The isomerism among compounds in which nitrogen is doubly linked 
to carbon is now so well established and the hypothesis of Hantzsch and 
Werner to explain it so abundantly supported by experimental evidence, 
that in this place it will suffice if a very brief statement of the most 
important conclusions arrived at be made, and attention called to a few 
points which cannot as yet be regarded as settled satisfactorily. 
(a) Ketoximes.—Goldschmidt! while working with V. Meyer on the 
oximes of benzil discovered an isomeride of benzil dioxime; later 
V. Meyer and Auwers discovered a third modification of the same 
substance? and a second monoxime of benzil.* Meyer and Auwers gave 
a clear and conclusive demonstration of the structural identity of these 
oximes‘ and proposed to account for their existence by assuming that 
free rotation between the carbon atoms was prevented in these compounds. 
The discovery of an isomeric oxime of p-chlor-benzophenone ® disposed of 
this view, which cannot account for the existence of a second oxime, and 
the hypothesis of Hantzsch and Werner © alone remained. 
These authors explain the isomerism of oximes by supposing that 
when a nitrogen atom is united to carbon by a double bond, the third 
valency is not in the same plane as the other two, and the group attached 
to it may take up two equilibrium positions one on either side of this plane. 
According to this hypothesis, there should be one oxime of 
a a—C—a 
co namely | 
a N—OH 
ine a—C—b a—C—b 
and two of CO namely | and | 
Be NOH HON, 
a prediction verified for the oximes of benzophenone and p-chlor-benzo- 
phenone and in many other cases. 
a—C—C—a 
Then two monoximes and three dioximes of a diketone eral 
0 Fa 
should exist, the dioximes being represented thus : 
a—C—C—a a—C C—a a—C — C-—a 
ll ll | I | I 
HON N.OH HON HON NOH HON 
which has been verified in the case of the mono- and dioximes of benzil. 
The isomerism in all these cases is perfectly definite, the compounds 
differing in melting point, crystalline form, solubility, and some of their 
chemical reactions, and further are mutually transformable under the 
influence of heat, solvents, and suitable reagents such as acids and 
alkalies. 
The usual criterion for determining their configurations is the 
1 Rer., 1883, 16, 2176. 2 Ber., 1889, 22, 537. 3 Ber., 1889, 22, 705. 
+ Ber., 1888, 21, 784, 2510: 1889, 22, 564, 1985, 1996. 
° Ber., 1890, 28, 2403. ° Ber., 1890, 28, 11; Zeit. phys. Chem., 10, 1. 
