249 



\\ . tiiul .in analogous case of the presence of such a mini 

 in tlu- moliruk', if we consider the following configuration: 



The symmetry is here C 4 ; but if the two groups X linked at tin 

 same carbon-atom be made different (e.g. X and//), the mirror-axis 

 A 4 will disappear, and the molecule, being now completely asymmetri- 

 cal, may be resolved eventually into optically active antipodes. 



Even if the molecule had simply the formula: 



/CH 2 \ /CH 2 \ 

 X H C< >C< >C H X 



\CH 2 / \CH 2 / 



the possibility of a separation into antipodes will be present. l ) 

 If in the cases of fig. 165 and 166, one or two of the asymmetric 

 carbon-atoms are changed into higher symmetrical radicals, the 

 molecules obtained will be resolvable, notwithstanding the fact that 

 the number of asymmetric carbon-atoms is now diminished. 



23. Should there be also a pseudo-asymmetric carbon-atom 

 in the ring, then the number of optically inactive, non-resolvable 

 isomerides will be increased, exactly as in the case of the open- 

 chain-derivatives formerly discussed. 



Thus Wislicenus succeeded in obtaining 'three isomerides of 

 2-5-dimethyl-cyclopentane-i-carboxylic acids. 2 ) Two of them are 

 cts-a's-forms (/ and //; mpts: 30C, resp. 77C), and as each of them 

 has the symmetry of the group S, they cannot be resolved into 

 optically active antipodes. That there are two of these "internally 

 compensated" isomerides, is explained by the fact that the carboh- 



superposable, the molecule has not the symmetry Dg, as perhaps would appear 

 at superficial examination, but that of group 4, as already mentioned. 



The conclusion of E. Mohr, Journ. f. prakt. Chem. (2). 68. 378. (1903), is 

 erroneous in this respect. 



1) O. Aschan, Ber. d. d. Chem. Ges. 85. 3396. (1902). 



2) J. Wislicenus, Ber. d. d. Chem. Ges. 84. 2572. (1901). 





