ON THE STEREOCHEMISTRY OF NITROGEN. Wye 
alike structure. A search for these isomerides instituted by Hantzsch and 
others has been successful in a number of cases. In all these casesit is 
more difficult to exclude the possibility of dimorphism and to show that 
the compounds in question are structurally identical. 
(c) Hydrazones and Semicarbazones.—The evidence for the existence 
of isomerism among hydrazones and semicarbazones is fairly conclusive, 
though by no means so satisfactory as for the oximes. 
Fehrlin ! found that the hydrazone of o-nitro-phenyl-glyoxylic acid was 
converted into an isomeride, when dissolved in alkalies and precipitated 
by the addition of acids ; the two products differed in crystalline appear- 
ance, melting point, solubility, and behaviour with nitric acid, but gave 
the same reduction product. These results were confirmed by Krause,” 
who found, besides, that both gave hydrazones of isatin on oxidation. 
Hantzsch and Kraft* by the action of phenyl-hydrazine on anisy]- 
phenyl-ketone on the one hand, and on its dichloride on the other, obtained 
two different anisyl-phenyl-ketone hydrazones which differed in appear- 
ance and solubility, and one of which was slowly transformed into the 
other in alcoholic solution. 
The possibility of structural differences was finally excluded by 
Overton * by preparing two diphenyl-hydrazones of anisyl-phenyl-ketone, 
and of p-tolyl-phenyl-ketone by the method used by Hantzsch ; several 
other hydrazones, however, could only be obtained in one form. 
Anschiitz and Pauly ° prepared three isomeric diphenyl-hydrazones of 
dioxy-tartaric ester, two of which are readily transformed into the third 
by heating in solution or by traces of reagents such as iodine and sulphur 
dioxide: behaviour which is very characteristic of stereoisomerides ; 
Bamberger and Schmidt ® found that two hydrazones of benzoyl-formalde- 
hyde could be obtained, and that these were interconvertible by means of 
solvents. 
The only aldehyde hydrazones which have been obtained in different 
forms are the phenyl-hydrazones of protocatechuic aldehyde,’ and of 
salicylic aldehyde,* and in both these cases the evidence is not sufficient 
to exclude the possibility of tautomerism in the benzene ring like that 
shown by phloroglucin. 
The evidence of the existence of isomeric semicarbazones is insufti- 
cient ; but Marckwald” has observed very definite isomerides of diphenyl 
thiosemicarbazine itself, which differ in melting point and in their 
reaction with carbonyl chloride. Their reactions are explained as 
follows :— 
C,H,NH—C—SH -. C,H,—NH—C—SH 
I I 
C,;H,—NH—N N—NH—C,H, 
| coal, | cocl, 
C,H;N—C—SH ne eS me 
CO N Now 
at ie ae —C,H,. P 
1 Ber., 1890, 23, 1574. 2 Ber., 1890, 28, 3617. 3 Ber., 1891, 24, 3511. 
4 Ber., 1893, 26, 18; see also Hantzsch, Ber., 26, 1. * Ber., 1895, 28, 64. 
® Ber., 1901, 34, 2001. 7 Wegscheider, Monats., 1893, 14, 386. 
§ Biltz, Ber., 1894, 27, 2288, ° Ber., 1892, 25, 3098. 
1904. N 
