ON THE STEREOCHEMISTRY OF NITROGEN. 187 
the ‘cubic’ one suggested by van’t Hoff in 1878,! in which the nitrogen 
atom is supposed to be at the centre of a cube and the five groups at five 
corners, thus : 
The disposition of the valencies would have to be altered to meet the 
requirements of recent experiments. 
The number of isomerides required by this configuration is usually 
larger than by some of the others on account of the lower degree of 
symmetry which it possesses, and, since it has no special advantages, little 
use has been made of it. 
(c) The ‘ Double Tetrahedron’ Configuration.—The next configuration 
which was proposed is usually called the ‘double tetrahedron’ configuration 
and associated with the name of Willgerodt.2 According to this view it 
is assumed that the two new groups are attached at right angles to the 
plane of the three already present, thus giving rise to an arrangement like a 
double tetrahedron. This arrangement has the highest degree of symmetry 
Fi4, 2. 
4 
> 
of any ; it requires the existence of (1) two isomerides of the type Na,X— 
namely, those in which a and 6 respectively occupy one apex while X 
occupies the other ; (2) three isomerides of the type Na.bcX, one of 
which should exist in optical antimers ; and (3) four isomerides of the 
type NabedX, all of which should exist in optically active forms. 
» Ansichten tiber Org. Chem., i. 80. 2 Journ. prakt. Chem., 1890, 41, 291. 
