188 REPORT—1904, 
(d) The ‘ Pyramidal’ Configuration—Behrend! discussed other 
possible arrangements of the five groups, and Bischoff” proposed the 
‘ pyramidal’ configuration in which the five groups are supposed to be 
situated at the angular points of a pyramid on a square base, the acidic 
radical occupying the apex thus : 
Fig. 3. 
5 
LOUD. oy aa 
1 4 
Considering this arrangement as originally suggested we should expect 
(1) no isomerides of the type Na,bX ; (2) two isomerides of the type 
Na,beX, one of which would be capable of existing in enantiomorphously 
related forms ; and (3) three isomerides of the type NabcdX, all of which 
should be capable of existing in optically active forms. 
It is evident, however, that this view must be modified somewhat, 
for, since it does not represent the three groups in tervalent nitrogen 
compounds in one plane, there are three possibilities : (a) a change of 
valency direction occurs ; (2) the acidic radical does not occupy the apex 
(this assumption increases the number of possible isomerides very con- 
siderably) ; (c) an interchange of position between two groups occurs 
during the change of valency. 
It is desirable to avoid the first assumption, if possible ; the last two 
have been made by Professor Kipping to account for the isomerism of the 
hydrindamine salts, and will be discussed in detail. 
(e) Only the Pyramidal Configuration accounts for the Facts.—To 
decide between these various views we have the following facts which 
must be accounted for : 
(1) The existence of stable, optically active compounds. 
(2) The existence of the isomeric hydrindamine salts. 
(3) The existence of isomerides of the type Na,bcX only in the case 
recorded by Aschan, and the optical inactivity of all these compounds. 
All the views account for (1), but the ‘double tetrahedron’ configura- 
tion does not account for (2), since both the new groups introduced during 
the change of valency are situated in the same plane symmetrically with 
reference to the existing groups, and are interchangeable by rotation.* 
1 Ber., 1890, 28, 454. 2 Ber., 1890, 23, 1972. 
8 See Trans. Chem. Soc., 88, 949. 
