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stereoisomers. He points out that all the substances of this type 

 thus far prepared have been prepared from tervalent compounds 

 of the type N, a, b, c ; and when we add a substance like d x to 

 it, the new group d chooses that position with respect to the 

 already existing radicals which produces the most stable con- 

 figuration. He starts with the plane formula of tervalent 

 nitrogen, and ends with the pyramidal formula for the penta- 

 valent nitrogen. He represents the changes thus : 



-> 



><J 



P^ 



The last two configurations are enantiomorphous and represent 

 the d- and 1- modifications of the one stable isomer. 



Jones's theory gives an ingenious explanation of the absence 

 of stereo-isomers ; but the weak point in his theory is that it 

 does not give an adequate explanation of the deviation of the 

 nitrogen-bonds from their original arrangement in one plane 

 into two different directions as represented above. In fact, his 

 hypothesis is open to the same objection as the Hantzsch- 

 Werner hypothesis. 



It has been shown above, while discussing the formula of 

 tervalent nitrogen, that we may assign a tetrahedral configuration 

 to it, if any facts demand it, in spite of the fact that no tervalent 

 nitrogen compounds show optical activity ; and so there is no 

 difficulty about the whole question at all. 



If we assume with Jones that the most stable configuration 

 results by the addition of d x to N, a, b, c, the change from 

 tervalent to pentavalent nitrogen, with only one pair of 

 enantiomorphs being formed, can be very simply represented 

 as follows : 



