STEREOISOMERISM AND OPTICAL ACTIVITY 245 



Pentavalent Nitrogen 



If one has to suggest a possible configuration for a compound 

 containing pentavalent nitrogen, one must bear in mind all the 

 facts which are known at present, and which it must satis- 

 factorily explain. One has to take the following facts into 

 consideration, viz. (1) existence or non-existence of optical 

 isomers in the different types, (2) existence or non-existence of 

 ordinary stereo-isomers, and finally (3) derivation from tervalent 

 nitrogen. 



Various configurations have been suggested ; but we need 

 not discuss all of them here. The one that explains the facts 

 most satisfactorily, and is therefore most in vogue, is the 

 pyramidal formula of Bischoff. 



a^ v d 



Let us see how it works out in the different cases. 



For convenience, let us consider the type N, a, b, c, d, x, first. 

 Optically active substances of this type have now been con- 

 clusively proved to exist, and Bischoffs formula, as can be 

 easily seen, accounts for the optical activity ; but the formula 

 demands two stereo-isomers (each being divisible into d- and 1- 

 enantiomorphs) that are not yet known to exist. 



X X 



ri 



H- 



N 



a. 



d 



Further, there is the difficulty of deriving it from the generally 

 accepted plane configuration of tervalent nitrogen. 



H. O. Jones 1 has attempted to explain the absence of the two 



1 Trans. Chem. Soc. 1903, 1403; 1905, 1721. 



