20 Kansas Academy of Science. 



and arrangement of the various elements and groupings which are 

 to be combined in such a manner as to produce the desired specific 

 results. 



The distinguishing characteristic in the structure of the opti- 

 cally|active organic substances is that they contain at least one car- 

 bon atom which is combined with four different atoms or groups. 

 If we consider the space distribution of the four different atoms or 

 groups about the central carbon atom we shall find that two ar- 

 rangements are possible. The two resulting forms are related to 

 each other in the same manner as an asymmetric object and its 

 mirror image. Such a carbon atom is called an asymmetric carbon 

 atom. We have for each substance containing such an asymmetric 

 carbon atom the possibilities of a right-handed st'-ucture and a 

 left-handed structure. Corresponding to these theoretical struc- 

 tures we find that nature has furnished us with dextrorotatory and 

 IfBvorotatory isomeric substances, which are closely identical in 

 all of their physical and chemical properties, but differing chiefly 

 in that the one rotates the plane of polarized light as far to the 

 right as the other does to the left. When these two so-called 

 sterioisomeric substances are mixed in equal quantities the result- 

 ing product is inactive. So, also, when two asymmetric carbon 

 atoms occur within the same molecule, inactivity may result from 

 internal compensation. It is thus found that among substances 

 of asymmetric structure there are two classes which arc optically 

 inactive. The members of the one class — said to be inactive by 

 internal compensation — are not separable into active components, 

 while the members of the other class — said to be inactive by ex- 

 ternal compensation — are separable into dextrorotatory and Isevo- 

 Totatory components. 



We have three methods for the separation of the optically active 

 -components, all of which are due to the researches of Pasteur. ^^ 



i. In some instances enantiomorphic crystals may be formed 

 which may be mechanically separated. 



2. By the aid of suitable active substances compounds may be 

 formed which differ in their solubility, thus permitting the two 

 optical isomers to be separated by fractional crystallization. 



3. Through the action of certain microorganisms one of the 

 optical isomers may be destroyed by fermentation while the other 

 remains unaffected. 



The direct synthesis of optically active substances from inactive 

 material has not been effected, because both of the stereoisomeric 



15. "Researches on the Molecular Asymmetry of Natural Orgranic Products," by Louis 

 Pasteur (1860); Alembic Club Reprint No. 14. 



