242 SCIENCE PROGRESS 



PART III.-COMPOUNDS OF NITROGEN 



Tervalent Nitrogen 



When we consider a compound, in which a nitrogen atom is 

 linked to three univalent atoms or groups, two configurational 

 formulae at once suggest themselves to us. The first is the plane 

 formula, in which all the valencies lie in the same plane. The 

 second is the tetrahedral formula, in which the nitrogen occupies 

 one corner of the tetrahedron, and the three atoms or groups the 

 remaining corners, the valencies being directed along the edges. 

 Facts must decide which of these two is the more probable one. 



According to the usual idea, the tetrahedral formula necessi- 

 tates the existence of optical isomers, when all the three groups 

 attached to the nitrogen are different. But all attempts made 

 up till now to resolve substances of that kind into optical 

 isomers have invariably failed. Neither are there any facts that 

 give any hope of success in the matter. So the general tendency 

 now is towards giving up the tetrahedral formula, and accepting 

 the plane one. 



On the other hand, there are many facts that tell against the 

 plane configuration. The most important of these is the existence 

 of two isomers in case of substances like aldoximes, ketoximes, 

 hydrazones, etc., and the diazo-compounds. It has been con- 

 clusively proved that the isomers in each of these cases are 

 structurally identical, and must therefore be stereo-isomers, and 

 the hypothesis of Hantzsch and Werner 1 is generally accepted 

 as the true explanation of the isomerism. Hantzsch and Werner 

 assign the following configurations to the isomers in the different 

 cases : 



