STEREOISOMERISM AND OPTICAL ACTIVITY 249 



in anhydrous benzene, in which solvent they can only be present 

 as true oxides. 



The optical activity in this case is easily explained. The 

 oxygen is linked up to two nitrogen-bonds ; these were originally 

 at an angle, but may now be supposed to be practically parallel 

 and very close to each other — in fact, equivalent to one bond 

 as far as the spatial arrangement of groups or radicals is con- 

 cerned. The whole structure thus becomes tetrahedral, exactly 

 like the carbon structure ; and as the four radicals are different, 

 optical activity is to be expected. 



Conclusion 



In the foregoing pages the writer has tried to show that the 

 idea that optical activity is not a result of enantiomorphism, but 

 that both of them (where they coexist) are results of another 

 structural cause, viz. the screw-spiral arrangement, although 

 recognised by crystallographists, has been ignored entirely by 

 chemists, in spite of the fact that what holds good in crystallo- 

 graphy, as regards optical activity, must also hold good in 

 chemistry, with this difference, that while the crystallographist 

 deals with the arrangement of molecules (or some other higher 

 units) in the crystal structure, the chemist deals with the 

 arrangement of atoms within the molecule itself. He has further 

 tried to show that the same idea can be successfully applied in 

 chemistry, giving illustrations from the various types of com- 

 pounds of carbon and nitrogen. For this purpose he has made 

 certain assumptions, drawn certain deductions from them, and 

 has even ventured on a prediction. If that prediction is not 

 fulfilled, or if those assumptions are found to be untenable on 

 other grounds, they will have to be abandoned ; and with them 

 the particular way, here suggested, of conceiving the screw- 

 spiral structure must also go. But some other way must be 

 found, or some cause of optical activity other than screw-spiral 

 arrangement must be postulated ; because we can hardly regard 

 enantiomorphism as the cause of optical activity, in the face of 

 the enantiomorphous but optically inactive crystals of barium 

 nitrate. 



