251 



which, according, to Wyrouboff 1 ), crystallises in the 

 (lass of the monoclinic system, two optical antipodes: 



an- known, which crystallise (+ 2H Z O) in the rhombic system, 

 although no hemihedral forms could hitherto be obtained. The 

 molecule of this cyclic compound does not possess, properly speaking, 

 an asymmetric carbon-atom at all, at least not in the sense of Van 

 't Hof f's and Le Bel's theory. The whole configuration however is 

 such that there is only a single binary axis of the first order, the direc- 

 tion of which is indicated in the formula by a dotted line. The sym- 

 metry of both molecules is therefore that of the cyclic group C 2 ; 

 the atomistic arrangement, having thus only axial symmetry, must 

 be different from its mirror-image, and the occurrence of the dextro- 

 and laevogyratory forms of inosite is in this way easily explained, 

 notwithstanding the fact, mentioned above, that no true asymmetric 

 carbon-atoms are really present. 



Of course optically inactive, non-resolvable modifications will be 

 possible too in the case of the inosites. If the substitutes be placed 

 as follows for instance: 



or 



OH 



T. 



n. 



the symmetry of these molecules is a rather high one : in a compound 

 of formula 7, there is a homopolar trigonal axis perpendicular to the 

 plane of the ring, three homopolar binary axes (including 60) in 

 the plane of the ring, and three "vertical planes of symmetry passing 

 through the trigonal axis and bisecting the angle between two suc- 



1) G. Wyrouboff, Bull, de la Soc. Miner. 25. 169. (1902). 





