208 



liEPORT — 1902. 



Hantzsch adopts the space formulae employed in explaining the isomerism 

 of the oximes. 



The assumption involved is that the valencies of the trivalent nitrogen 

 atom are directed along the convergent edges of a regular tetrahedron, 

 the atom itself being situated at the apex of the solid angle thus pro- 

 duced. 



When two nitrogen atoms become doubly linked in a molecule, the 

 compound which results is capable of existing in two stereomeric forms 

 corresponding with the diagrams I« and II. 



By means of these diagrams the syn- and an<i-diazo derivatives may 

 be compared with the stereomeric oximes and the cis- and <?-«ris-isomerides 

 of doubly-linked carbon compounds. 



The great instability of the syn-diazo series may be explained in terms 

 of v. Baeyer's ' tension ' theory. According to this hypothesis, the 

 valencies linking together two conjugated atoms tend to set themselves 

 in the same straight line, and when this is not possible, a stress is pro- 

 duced in the molecule which renders it unstable and prone to undergo 

 rearrangement. 



The diagram la indicates a molecule in this unstable condition, the 

 linking A'alencies of the two nitrogen atoms being inclined at an angle to 

 each other. This intramolecular strain can be relieved by placing the 

 sides of the tetrahedra bounded by continuous lines in the same plane, 

 the necessary change in the spatial relationship of these figures being 



