276 



figuration, the slow one with a re-arrangement of the atoms 

 in space. 



Mercuric oxide also seems to act upon haloginated acids in the 

 same way as silver-oxide. 



The change of an ammo-acid into an hydroxy-a.cid by means 

 of nitrous acid, is a very quick reaction; therefore no change of 

 configuration would take place here, and Biilmann concludes 

 that the aspartic acid and the malic acid in plants would have 

 the same arrangement in space of the groups placed round the 

 asymmetric carbon-atom. 



4. But here we touch the problem under consideration at 

 its very crux: for how can we be sure whether the original 

 asymmetrical configuration has- been changed during the process 

 or not? If the reactions without change of configuration be 

 named normal, and those accompanied by such a change abnormal 

 substitutions, we may ask: when must a chemical reaction be 

 considered as a normal and when as an abnormal one? 



The answer to this question has occupied a number of chemists, 

 because it is evidently closely related to the particular views on 

 the mechanism of substitution in such asymmetric molecules, and 

 several explanations of the W a 1 d e n-in version have been suggested 

 by various authors. l ) 



Some of them, especially Armstrong, Gadamer, and 

 Fischer, make the supposition that during the reaction in'stable 

 intermediate compounds must necessarily be formed, in order to 

 preserve a continuous asymmetry of the molecule, while the 

 substitution takes place; and Fischer points out, that precisely 

 the substitutes NH 2 , OH, Cl, etc., with which the W a 1 d e n-in ver- 

 sion ordinarily occurs, are those which have a "residual affinity". 

 This enables them to form such intermediate compounds, which 

 are then later decomposed, and the place vacated by the old 



1) H. E. Armstrong, Journ. Chem. Soc. London, 69. 838, 1399. (1896); E. 

 Fischer, Berl. Ber. 40. 492. (1907); Ann. der Chemie 381. 312. (1911) 386.374. 

 (1911); 394. 352. (1911); J. Gadamer, Chem. Zeitg. 34. 1004. (1910); 36. 1327. 

 (1912); J. A. Le Bel, Journal de Chim. phys. 9. 323. (1911); A. Werner, Ber. 

 d. d. Chem. Ges. 44. 873. (1911). E. Biilmann, loco cit.; P. F. Frankland, 

 loco cit. p. 738; cf. also: G. Senter, Journ. Chem. Soc. London, 107, 638. 

 (1915); 109. 1091. (1916); S. Arrhenius, Theorien der Chemie, 2e Aufl. (1909), 

 p. 83; E. Mohr, Chem. Zeitg. 36. 984. (1912); P. Pfeiffer, Lieb. Ann. 383. 

 123. (1911). 



