CONFIG UR A TION 9 1 



positions of the atoms, i. e. the structure of the molecule, 

 in the literal sense of the word, is included under 

 configuration. 



We will first describe the methods applied, and then 

 devote a special section to stereochemistry, which developed 

 through their application. 



The two methods are essentially the following : 



A. Determination of configuration by the number of 

 isomeric derivatives. 



B. Determination of relative distances in the molecule. 

 The first method especially has led to valuable results ; 



the second is at present chiefly of importance for its 

 intrinsic scientific meaning. 



A. Determination of Configuration by the Number of 

 Isomeric Derivatives. 



The wide applicability of the principle now to be 

 discussed will be best appreciated by particular examples, 

 of which cases may be chosen illustrating the fundamental 

 meaning of the method. Such examples are those referring 

 to the constitution of the benzene derivatives, and to 

 stereochemistry. 



i. Constitution of Benzene 1 . 



The molecular formula of benzene, C 6 H 6 , allows of 

 a large number of structural formulae in accordance with 

 the indications of the theory of valency, and possessing an 

 equal degree of probability. Several isomers, such as 

 dipropargyl, are in this way possible. 



The choice was made by Kekule on the ground of the 

 number of isomeric derivatives, in particular because the 

 monosubstituted bodies C 6 H 5 X, such as phenol. C 6 H 5 OH, 

 exist in only one form, the disubstituted C G H 4 XY, such as 

 oxybenzoic acid, C 6 H 4 (OH)(COOH), in three isomeric forms. 



1 Marckwald, Die Benzoltheoriej 1897 ; Vaubel, Der Benzolkern, 1898. 



