238 SCIENCE PROGRESS 



difference is not far to seek. It is the same which gives rise to 

 other differences between saturated open-chain and ring-com- 

 pounds, like cis-trans-isomerism ; viz. that ring- formation 

 deprives the two end-carbons of a chain of their free rotation. 

 The writer has nowhere seen this difference put in the form 

 which is here given to it. It usually appears in another form, 

 viz. in the distinction that is drawn between ordinary asym- 

 metry, where it can be referred as being due to a particular 

 asymmetric carbon, and 



The so-called Molecular Asymmetry 



where it is not so referable, as for example, in the case of 

 inosites. This distinction is considered by many chemists to be 

 unnecessary and even illogical ; and so it appears, when stated 

 in such a form ; because all optically active molecules are asym- 

 metric, whether they contain an asymmetric carbon or not. 

 Further, it is to be noted that all substances whose activity is 

 alleged to be due to the asymmetry of the molecule as a whole, 

 are ring-compounds (the only open-chain grouping, which, if 

 realised, will fall in this category, is the allene grouping, 

 which will be fully discussed presently). For these reasons, it 

 appears to the writer both logical and convenient to state this 

 difference as a difference between saturated open-chain- and ring- 

 compounds. 



This can be further illustrated by taking a concrete example, 

 which has been a subject of great controversy recently. In 1909, 

 Perkin, Pope, and Wallach l synthesised 



i-Methyl-cyclohexylidene-4-Acetic Acid 



CHj-, /CH 2 CH 2 \ /H 



\q/ ' )C:::::::;;(/ 



H / '\cH, CH,/ >N \COOH 



(1) (4) (7) 



which they subsequently succeeded in resolving into optical 

 isomers. 



[In the configuration, all the linkages represented by whole 

 lines lie in one plane, while the linkages represented by the 

 dotted lines lie in a plane at right angles to the first, according 

 to the Van't Hoff view, and in any other plane or planes, accord- 

 ing to the writer's view.] 



1 Trans. Chetn. Soc. 1909, 1789. 



