I2 4 



MOLECULAR STRUCTURE 



Ring formation. Finally we may consider the leading 

 conclusion of stereochemistry as applied to the formation 

 of rings, and in particular to the case of trimethylene 

 dicarboxylic acid, 



H 2 C HCCOOH 



HCCOOH. 



Representing such a ring in the following way : 



with the six attached groups at i to 6, there are these 

 possibilities : 



No. 2. 



II 



No 3. 

 II 



II /|\ COOH COOH /\\ II 

 II Xl /H 



II 



II 



COOH 



COOH COOH COOH 



Formula i represents a symmetrical, and therefore inactive 

 form ; Nos. 2 and 3 a pair of asymmetrical images, 

 consequently active. Actually two inactive isomers are 

 known, of which perhaps one is the unseparated mixture 

 or racemic compound of Nos. 2 and 3. 



4. Stereochemistry of other Elements. 



The spatial considerations applied with so much success 

 to the carbon compounds may be extended to compounds of 

 other elements. We will here only mention what refers to 

 nitrogenous bodies. 



First must be considered the possibility of separation 

 into optical antipodes, suggested by Le Bel in the case of 

 isobutylpropylethylmethylammonium chloride : unfortu- 

 nately the researches on this point are only fragmentary, 



