ON OUR PRESENT KNOWLEDGE OF AROMATIC DIAZO-COMPOUNDS. 207 



Addendum, 



I. Additional Notes on the Stereochemical Theory. — Since ■writing the 

 foregoing report the author has received a communication from Professor* 

 Hantzsch containing the latest developments of the stereochemistry of 

 the diazo-compounds. 



The alternative views are fully discussed and the plane jformulre sug- 

 gested for the syn- Amzo derivatives, on the assumption that these sub- 

 stances diflfer structurally from their an<i-isomerides, are shown to be 

 incapable of accounting for the observed facts. 



In addition to the diazonium formula, three other structualj formulsd 

 have been advanced for the metallic si/n-diazo-oxides : 



R.N.NO R.N - N.Na R.N:N.Na 



I \/ II 



Na O O 



These configurations fail, in the following important points, to account 

 for the behaviour of these metallic diazo -derivatives : 



1. They do not furnish a simple explanation of the reciprocal trans- 

 formation of these substances into diazonium salts and vice versd, 



2. They do not indicate that capacity for coupling with phenols to form 

 azo-compounds, which is so essentially characteristic of the syw-diazo 

 series. 



3. Moreover, they involve the additional assumption that the 

 isomerism of the metallic diazo-oxides ditfers essentially from that of the 

 diazo-cyanides and diazo-sulphonates, inasmuch as the latter compounds 

 cannot be formulated on these lines. This hypothesis is, however, un- 

 justifiable for the sy 11- Ai-Azo derivatives of the three Series (oxides, cyanides, 

 and sulphonates) have comparable properties. 



The only other structurally dissimilar fornlulfe available for the syn- 

 diazo-cyanides and diazo-sulphonates are the diazonium formula 



R.N.CN(S03K) 



N 



and the configuration R.N . N.CN(S03K). 



The former of these is not in accordance with the general properties 

 (colour and sparing solubility) of these dei-ivatives, and moreover the 

 electrolytic dissociation of the diazo-sulphonates into two ions confirms 

 the view that the compounds are diazo-sulphonates, R.N:N.S03K, and not 

 diazonium sulphites. 



The second formula involves an entirely new assumption — namely, that 

 of isomerism due to change of valency ; but even if this possibility be 

 granted, the corresponding formulation does not furnish an explanation 

 of the close relationship existing between the syn and anti series, for the 

 isomeric pairs of diazo-compounds, 



RN:N.CN(S03K)and RN:N.CN(S03K), 



being derivatives of pentavalent and trivalent nitrogen respectively, ouo-ht 

 to ditfer completely in their chemical reactions. 



In developing the stereochemical theory of the diazo-derivatives, 



