STEREOCHEMISTRY 103 



recognized as such. It was Wislicenus who first, in 1873, 

 moved by the discovery of the isomeric active ethylidene- 

 lactic acids, CH 3 CHOHCOOH, expressed himself convinced 

 that the usual constitutional formulae do not suffice to 

 elucidate this isomerism. 



Some extension of the theory of constitution was thus 

 necessary, and of the three possibilities, dissimilarity in the 

 valencies of carbon, displacement of the atoms, and the 

 relative position of the atoms in space, the last, as is well 

 known, turned out to be the satisfactory explanation 1 . 



Dissimilarity between the different valencies of the 

 carbon atom is not suited to supply the explanation, 

 because that assumption would require isomerism in even 

 the simplest derivatives of the type C(X) 3 Y, such as 

 chlormethane, CH 3 C1. It is of importance that Henry 2 

 carried out a systematic research on this point, preparing 

 nitromethane, H 3 CNO.,, in four different ways, each of which 

 would have brought the nitro group into the place of 

 a different carbon atom. If, then, we distinguish the four 

 hydrogen atoms by the indices abed, he prepared 



C(N0 2 ) fl H 6 c d , CH tt (N0 2 ) 6 H c * CH a 6 (NO 2 ) C H rf , 

 and CH a6c (N0 2 ),, 



which turned out to be identical. 



The starting material for this was methyl iodide, 

 CI a H 6 c d : this, combined directly with Ag NO 2 , was trans- 

 formed into C(NO 2 ) a H &C rf. Another portion was converted 

 by KCN into the nitril of acetic acid, C(CN) a H 6 c d , and then 

 into acetic acid itself, C(COOH) a H fe c d ] this was chlorinated 

 to C(COOH) a Cl 6 H crf , and on treatment with AgNO 2 

 gave, through the transiently formed nitroacetic acid, 

 C(COOH) a (N0 2 ) 6 H cd , the second nitromethane, CH a (NO 2 ) 6 

 H cd . Another portion of the nitroacetic acid was then 

 converted into malonic acid, chlorinated to C(COOH) a6 

 Cl c H d , and reduced by AgN0 2 to the third nitromethane, 



1 Van 't Hoff, Lagerung der Atome im Raume (2nd ed.), 1894. 



2 Zeitschr.f. Phys. Chem. 2. 553. 



