ORGANIC CHEMISTRY i95 



Baxter and Parsons {J.A.C.S., 1920, 43, 507) show that 

 meteoric has the same atomic weight as terrestrial nickel. 



ORGANIC CHEMISTRY. By O. L. Brady, D.Sc, F.I.C. University 

 College, London. 



New Types of Isomerism. — The preparation and investigation 

 of an increasingly large number of organic compounds is bring- 

 ing to light types of isomerism which cannot be explained by 

 means of the usual structural formulae. 



As early as 191 2 Cain and his co-workers showed that the 

 dinitrobenzidine prepared by Bandrowski by the nitration of 

 diphthalyl-benzidine was not identical with that of Strakosch, 

 obtained by the nitration of diacetyl-benzidine, although both 

 contain the nitro-groups ortho to the amino-groups. The 

 orientation of these two compounds has been established by 

 their oxidation to 3 nitro-4 acetylamino-benzoic acid, and by 

 their reduction and condensation with benzil to yield the same 

 diquinaldine. 



7 



The isomerism is explained by these authors by supposing 

 that in Kaufler's formula for diphenyl [I] the two phenyl 

 rings are incapable of free rotation ; it follows that two stereo- 

 isomeric dinitrobenzidines could be obtained both ortho- 

 substituted to the amino-group, namely, a 3 : 3'-dinitro- and a 

 3 : 5'-dinitro-compound which can be represented in a plane 

 thus : 



Adopting the view that in general symmetrical compounds 

 have a higher melting-point than unsymmetrical, formula [II] 

 has been assigned to Bandrowski's, and formula [III] to 

 Strakosch 's dinitrobenzidine. 



The isomerism extends to the acyl derivatives of the two 

 dinitrobenzidines and to the dinitro-diphenyl obtained by 

 removal of the amino-group. The two compounds differ in 

 their behaviour in the Sandmeyer or Gattermann reaction. 



