339 

 CH = OH 

 CH, CH— CH = CH,. 



Tlie place of the double bonds in lliis compound is now exactly 

 known. The substance being optically active, an asymmetric carbon 

 atom must be present in it; a formula, e.g. as the following: 



CH,— CH,— C CH 



II II 



CH CH 



would not satisfy, as has also been remarked by Windaus. 



As «-vinyldihydrofurane is formed from mannitane tetra for- 

 mate, it is now possible to draw up a structure formula for the 

 anhydrides of mannitol, viz. mannitane and isomannide. 



We then arrive at the following scheme for mannitane: 



OH 



1 i I 



CH,— CH— CH— CH— CH— CH,OH. 



I I 

 OH OH 



In connection with the spatial formula of mannitol: 



OH OH 



I I 

 CH,OH— CH— CH— CH— CH— CH,OH 



I I 

 OH OH 



We see that as soon as the oxide-ring is formed between the C- 

 atoms 1 and 4, the OH-groups at 2 and 3 will be at the same 

 side. Besides the molecule contains two OH-groups situated beside 

 each other at 5 and 6 (in perfect accordance with the pyrogenic 

 decomposition of the tetra-formate, in which formic acid and carbon 

 dioxide are split off from OH-groups placedj beside each other), so 

 that here a possibility must be for the foimation of a di-acetone com- 

 pound, in fact this compound was obtained as a colourless substance 

 crystallizing in glossy leaflets, melting-point 155° (analysis C 58.83, 

 H8.38; calculated C 59.0 H 8.2). 



The conductivity of boric acid will also be increased greatly by 

 mannitane. M 



1) BöESEKEN, Rec. 40, 553 (1921). 



