THE SPACE RELATIONS OF ATOMS. 



459 



sentation of these relations is given by Van't Hoff in the 



figure. 



Fig. 13. 



Here the nitrogen occupies the centre of the cube, and 

 the five radicals connected with it occupy five of the corners. 

 Of these, 1, 2, and 3, which have like positions, represent 

 alkyls held by the three ordinary valences. When the nitro- 

 gen is tried these lie in one plane with the nitrogen atom; 

 in the figure they are shown nearer to 4, as they would 

 be attracted by the negative atom, say chlorine, occupying 

 that position. The fourth positive- group (alkyl) would 

 occupy 5. 



Now for the compound NR'R"R'"R iv Cl a symmetrical 

 arrangement is impossible. Four types are possible, as any 

 one of the four radicals may occupy 5, and each type 

 should be divisible into two isomers of opposite activity. 

 Already several isomers have been prepared in the case of 

 N.C 4 H 9 . C 3 H 7 . C 2 H 5 .CH 3 .C1. 



For N(R') 2 R" R'"C1 we may have either an asymmetric 

 configuration (R' in 5) or a symmetric configuration (R" or 

 R"' in 5), and the symmetrical being always the more 

 favoured compound it is the latter only which exists ; for 

 Le Bel found it impossible to divide these compounds into 

 active components. 



For NR 3 R"C1 two isomers are possible according as 

 R" occupies 5 or 1 (1 = 2 = 3). This is the isomerism just 

 mentioned as occurring in the case of N(CH 3 ) 3 . C 4 H 9 . CI. 



With regard to the literature of this subject, very full 



