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ORGANIC AGRICULTURAL CHEMISTRY 



carbon atom. Le Bel went no further than we have stated above. 

 van't Hoff, however, not only assumed this asymmetry of the 

 carbon atom as the explanation of optical activity and of the 

 existence of isomeric structurally identical compounds, but he 

 assumed a definite arrangement for such a carbon atom in 

 space. 



Tetrahedral Theory. — He assumed that tetravalent carbon 

 exists in space situated at the center of a regular tetrahedron 

 with the four equal valences directed toward the angles of each 

 apex as follows : 



Methane 



In methane all four valences are satisfied with hydrogen so 

 that the carbon and the whole compound is completely sym- 

 metrical. If, however, as in the lactic acids, these four va- 

 lences are satisfied by four different groups, then the carbon 

 atom would be asymmetric and the compound would possess 

 asymmetry possible of exhibiting itself in its action toward 

 polarized light. The formula would be: 



OH 



COOH HOOG 



Lactic acid 



CH., 



Such an arrangement would make possible a compound A and 

 a second compound B which differ in that one is right-handed 



