1903.] 



on Becent Advances in Stereochemistry. 



305 



chemical isomerides differ in chemical, physical and mechanical 

 respects. That carbon atom which was present in the original 

 methane molecule is, in these new compounds, now attached to four 

 different atomic groups, and such a carbon atom is termed an asym- 

 metric carbon atom. It is in the case of substances containing an 

 asymmetric carbon atom that a lack of agreement is observed 

 between the facts and the kind of isomerism indicated by the Kekule 

 formulae, and in these cases also the species of isomerism indicated 

 by the solid models exhibited is found to correspond closely with 

 the facts. 



To illustrate this, we may refer to a somewhat complicated 

 substance termed tetrahydroquinaldine, which has the appended con- 

 stitution and the molecule of which contains an asymmetric carbon 



H H 



H 



H-C 



% 



\ / 



H 



s / \ / 



C C— H 

 II I 



C C— H 

 ' \ /\ 

 N CH3 



H 



Tetrahydroquinaldine. 



atom, that, namely, which is printed in heavy type. Three different 

 isomeric forms of this substance exist and are quite indistinguishable 

 by any of the ordinary methods of chemical or physical identification ; 



Fig. 5. 



one of these is a loose kind of compound of the other two, and may 

 therefore be disregarded for the moment. The remaining two have the 

 same melting point, the same boiling point and correspond exactly in 

 all ordinary properties; they yield, however, series of derivatives 



