261 



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

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

 chain-derivatives formerly discussed. 



Thus, Wislicenus succeeded in obtaining three isomerides of 

 2-^ -dimethyl- cy clop entane- 1 -carboxylic acids. l ) Two of them are cis- 

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

 has the symmetry of the group 5, they cannot be resolved into 

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

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

 atom to which the group COOH is linked, is a pseudo-asymmetrical 

 one, while both the neighbouring carbon-atoms are really asymmetric. 



The third isomeride (///, mpt : 50C) is a cis-trans-form ; it must 

 represent a racemic compound, because its configuration is wholly 



I. 



asymmetrical (group A), and under favourable circumstances it 

 must, therefore, be possible to resolve it into two enantiomorphously 

 related components. Up till now this fission has, however, not been 

 performed. 



In this connection the investigations of Von Baeyer 2 ) and 

 Perkin 3 ) on the hexa-hydrophtalic-, -isophtalic- , and -terephtalic- 

 acids may be mentioned here. While both (cis-, and trans-) hexa- 

 hydro-terephtalic acids have the symmetry S, and thus are not 

 resolvable into optically active antipodes, while the same is the case 

 with the cis-isomerides of the corresponding phtalic-, and -isophtalic- 

 acids, the trans-hexa-hydrophtalic-, and the corresponding hexa- 

 hydro-isophtalic acids have, however, the axial symmetry of the 

 group C 2 . In accordance with this, Werner and Conrad 4 ) succeeded 



1) J. Wislicenus, Ber. d. d. Chem. Ges., 34, 2572, (1901). 



2 ) A. Von Baeyer, Ann. der Chemie, 245, 103, (1888); 251, 258, (1889); 258, 

 l; 145, (1890). 



3 ) W. H. Perkin Jr., Journ. Chem. Soc. London, 59, 798, (1891). 



*) A. Werner and H. E. Conrad, Ber. d. d. Chem. Ges., 32, 3046, (1899). 



