STEREOISOMERISM AND OPTICAL ACTIVITY 243 



Here the two nitrogen-bonds that join it to the carbon or the 

 other nitrogen are supposed to be in one plane, while the third 

 bond lies in a different plane. This creates a strong presumption 

 in favour of the tetrahedral formula. 



The hypothesis of Hantzsch and Werner, although it explained 

 the numerous phenomena in question in a beautifully simple 

 manner, did not make its way unopposed. Even now it is 

 accepted by chemists with considerable reserve. The reason is, 

 that it seems impossible to understand by what mysterious forces 

 the nitrogen-bonds are deviated from their normal arrangement 

 in one plane. 



Evidence of an interesting kind has been recently brought 

 forward by Mills and Bain, 1 in support of the Hantzsch-Werner 

 hypothesis. These workers prepared the oxime of cyclo-hexa- 

 none-4-carboxylic acid : 



H x /CH, CH 2X 



>C< >C:-_- ------- -.1 N . OH 



COOH/ \CH, CH/ 



(4) * (1) 



and found that this acid forms both dextro- and laevo-rotatory 

 salts of the alkali metals. Now in this configuration, whether 

 we consider the optical activity as due to the asymmetric C (4), 

 or we consider it as due to the asymmetry of the whole molecule, 

 its mere presence demands that the single bond joining OH to N 

 lies in a plane different from that of the other two bonds. This 

 fact obviously gives considerable support to the Hantzsch- 

 Werner hypothesis. 



So here there seems to be a dead-lock. One set of facts 

 requires one configuration for tervalent nitrogen, another set 

 requires another. Now let us see if the new hypothesis helps 

 us out of the difficulty. 



As has been mentioned above, it has been tacitly assumed 

 that a tetrahedral formula for tervalent nitrogen will require the 

 existence of optical isomers, when all the three groups attached 

 to it are different, because it will give two enantiomorphous 

 configurations. But we have seen already that this assumption 

 is not valid. Besides enantiomorphism, some sort of screw- 

 spiral structure must be present in the configuration, if it is to 

 show optical activity. 



1 Trans. Chan. Soc. 1910, 1866. 



