287 



Instances of this are wellknown: the salts of many optically 

 active acids show a rotation opposite to that of the acid itself, 

 and the same may be the case when organic optically active bases 

 are transformed into their salts by addition of ordinary in- 

 organic acids. 



Thus the zinc-salt of dextrogyratory lactic acid l ) is itself laevo- 

 gyratory, arid the same is true for the sodium-salt of dextrogyratory 

 ot-nitrocamphor ; laevogyratory glycerinic acid gives a dextrogyratory 

 calcium-salt 2 ). The chlorohydrate of dextrogyratory a-amino succinic 

 acid is laevogyratory 3 ; and the opposite rotations of the derivatives 

 of aspartic acid are wellknown, according as the H of the COOH-group 

 be replaced by metal-atoms, or that a salt be formed by addition of 

 an acid to the amino-group 4 ). In these cases the circumstances 

 during the chemical process are such as to make a rearrangement 

 of the original molecule highly improbable, because with a few pre- 

 cautions any change of temperature may be avoided. The problem 

 of -explaining the change of sign of the rotatory effect after sub- 

 stitution, cannot be solved at present, as we are still waiting for a 

 sufficient dynamical explanation of the molecular rotatory power 

 in its dependence on the dissymmetrical arrangement of the atoms 

 in the molecule. Here lies a problem of the highest interest and urgen- 

 cy for mathematical physicists, and it is to be hoped that some 

 advance will be made in this difficult matter within not too remote 

 a future. 



3. In this connection we have, however, to consider a pheno- 

 menon which is also of high importance for the problems with 

 which we shall have to deal further-on in this chapter. I mean 

 the remarkable inversion discovered by Walden 5 ) in 1896, and 

 which may best be elucidated by some examples. 



If in laevogyratory malic acid, the hydroxy /-group be replaced 

 by chlorine, a dextrogyratory chloro-succinic acid results. This in 

 itself is not particularly remarkable, because in accordance with 

 what has been said above, both substances can have analogous 



J ) E. Fischer and A. Skita, Zeits. f. physiol. Chemie, 33, 190, (1901). 



2 ) E. Fischer and W. A. Jacobs, Ber. d. d. Chem. Ges., 40, 1068, (1907). 



3 ) E. Fischer and K. Raske, Ber. d. d. Chem. Ges., 40, 1053, (1907). 



4 ) V. Meyer and P. Jacobson, Lehrb. d. Organ. Chemie, 2e Aufl., I, 2, 778, 

 779, (1913). 



5) P. Walden, Ber. d. d. Chem. Ges., 29, 133, (1896); 30,2795,3146, (1897); 

 32, 1833, 1855, (1899); 40, 2470, (1907); etc.; Optische Utnkehr-Erscheinungtn, 

 Braunschweig, (1919). 



