278 



doubtedly quite right, when he states: "it appears that there 

 does not exist at the present time any criterion by which the 

 relation between the configuration of an optically active compound 

 and that of its derivative, can be decisively ascertained." All 

 assumptions as to the occurrence or non-occurence of a change 

 of configuration during such a substitution, appear to be merely 

 arbitrary and hypothetical. 



Such assumptions for instance are: that the change of rotatory 

 power from positive to negative, and vice versa, if PC1 5 or PBr 5 

 act upon hydroxy-acids or their ethers, is really accompanied by 

 an inversion of the configuration round the asymmetric carbon- 

 atom; that eventually the same takes place when the halogen- 

 acids: HCl, HBr, etc., themselves act upon such hydroxy-acids 1 ); 

 that the same occurs when SOCl z acts upon such mulecules 2 ); 

 that NOBr and HN0 2 , acting upon amino-a.cids, do not cause a 

 change of configuration 3 ) ; that on the other hand the substitution 

 of NH 2 by a halogen-atom is commonly accompanied by a change 

 of configuration; etc. etc. 



The question is undoubtedly enormously complicated. In truth, 

 every substitution of an atom or radical by some other, must 

 always have a distortion of the molecule as a necessary conse- 

 quence; and every thing evidently depends on the relative effect 

 of this distortion in comparison with that necessary to cause a 

 real interchange of place leading to a consequent inversion of the 

 stereometrical arrangement round the asymmetric carbon-atom. 



The very important recent researches of S e n t e r 4 ) demonstrate 

 convincingly that the difficulty is much greater yet than has 

 been hitherto realised, and that the phenomenon itself is also 

 much more complicated than was thought at first. This author 

 found that, if in optically active ammonium-phenyl-chloro- acetate 

 the chlorine-atom is substituted by an amino-gToup, optically 

 active products will result, whose rotation is positive or negative, 

 according to the special nature of the solvent taken as reaction- 

 medium. He stated, for instance, that if water were used as a 



!) A. Me. Kenzie and H. B. P. Humpries, Journ. Chem. Soc. London 97. 

 121. (1910); A. Me. Kenzie and H. Wren, ibid. 97. 1355. (1910). 



2) A. Me. Kenzie and F. Barrow, Journ. Chem. Soc. London 99. 1923. (1911). 

 R. H. Pickard and J, Kenyon, Ber. d. d. Chem. Ges. 45. 1592. (1912). 



3 ) E. Biilmann, Ann. der Chemie 388, loco cit. (1911). 



4) G. Senter, Journ. Chem. Soc. London, 107. 638. (1915); 109. 1091. (1916). 



