178 REPORT—1904. 
Both react with methyl iodide to give derivatives in which the methy] 
group appears to be attached to sulphur, which points to the absence of 
structural differences. 
(d) Stereoisomeric Aniles and other Compounds.—Many unsuccessful 
attempts to prepare aniles, Schiff’s bases, in isomeric forms were made 
before any indication of their existence was obtained.! 
A new isomeride of ethylidene aniline was isolated by Hibner,? from 
the product of the reaction in water, which melted at 85°5° C., whereas 
that already known melted at 126°C. The two compounds are mono- 
molecular, and the one with the lower melting point is readily converted 
into the other. Later, the same chemist with Peltzer? isolated two 
isomeric ethylidene o-toluidines, which were apparently structurally iden- 
tical, and of which, again, the lower melting point form could be readily 
transformed into the higher. Hantzsch and Schwab ‘ described two ben- 
zylidene p-toluidines in which the isomeride with the lower melting point 
is the more stable. The possibility of structural differences in simple 
aniles, like C,H,—N=CH—CHsz, need scarcely be considered, and the 
relations between the compounds exclude dimorphism, so that their exist- 
ence must be due to stereoisomerism. 
Lastly, Schall and Raschkowetzky° describe two isomeric carbo- 
JN—CoHs 
diphenylimides, of , between which there can be no structural 
Aw -CyH; 
difference. 
a—N 
(e) Compounds of the type II Azo and Diazo Compounds.—Azo 
NN — ’ 
compounds ought to exist in isomerides similar to those of oximes and 
hydrazones, but that they do so has never been established in a satisfac- 
tory manner. Janowski® has described two trinitroazotoluenes and two 
p-azoxytoluenes ; the evidence, however, is insufficient to allow any defi- 
nite conclusion to be drawn from it. 
The diazo compounds are well known to exist in isomeric forms, to 
explain which no hypothesis seems adequate except that of Hantzsch, 
together with the admission of structural isomerism. This subject is so 
involved, and moreover has so recently formed the subject of an exhaus- 
tive report,’ that a mere mention must suffice. Syn and antidiazo com- 
pounds exist, which are represented thus 
C,H,;—N C;H,—N 
| and I 
X—N N-X, 
where X represents an acidic radical, a hydroxyl group, or a metallic 
radical attached to oxygen. Diazonium compounds, which are structurally 
different from the diazo compounds, also exist. 
a—C—b 
The existing isomerides of compounds of the type ll and allied 
N—c 
types can only be satisfactorily explained with the aid of the Hantzsch- 
1 Ber., 1891, 24, 3518; 25, 2020; Ann. Chem. Phys., 1896, 9, 433. 
2 Ber., 1894, 27, 1299. 2 Ber., 1900, 33, 3460. 
4 Ber., 1901, 34, 822. ® Ber., 1892, 25, 2880. 
6 Monats., 1888, 9, 831; 1889, 10, 583; Ber., 1890, 23, 1176. 
7 Morgan, Brit. Assoc. Rep., 1902, 181. 
