260 



first formula. Having thus a symmetry-element of the second order 

 in their atomistic arrangement, the configuration of the molecules 

 must be congruent with its mirror-image (group C 4 ), and, therefore, 

 no fission of the proposed kind can be possible here. l ) 



We find an analogous case of the presence of such a mirror-axis 

 in the molecule, if we consider the following configuration: 



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

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

 X 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: 



XHC 



CH 



CH 2 / \CH 



/CH 2 



CHX 



the possibility of a separation into antipodes must be present. 2 ) 



If in the cases of fig. i6j and 168, 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 asymmetrical carbon-atoms is now diminished. 



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



1 ) The groups (C(a6c)} are unsymmetrical, and thus are different from their 

 mirror-images. To avoid confusion, it is better, therefore, to discriminate them 

 pairwise by the prefixes d-, and /-; just because d-C(abc) and l-C(abc) (or: l-C(acb)) 



V 



are nonsuperposable, the molecule has not the symmetry D 2 or C 2 , as per- 

 haps would appear at superficial examination, but that of group C 4 , as already 

 mentioned. 



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

 erroneous in this respect. 



2 ) O. Aschan, Ber. d. d. Chem. Ges., 35, 3396, (1902). 



