CONSTITUENTS OF THE BIOSPHERE 



21 



Haworth's formulae take into account certain properties not immediately 

 apparent when the other formulae are used. For example, the a form of 



H OH 



\ / 

 C 



H— C— OH 



HO— C— H 



H— C— OH 



H— C 



O 



CHoOH 



a-D-glucopyranose 



H OH 



\ / 

 C 



H— C— OH 



HO— C— H 



H— C 



H— C— OH 



O 



CH2OH 



a-D-glucofuranose 



D-glucopyranose when heated yields an anhydride, a glucosan formed by 

 elimination of water between the hydroxyl of C-1 and the hydroxyl of 

 C-2: 



CH.OH 



O H 



OH "N... y^ OH 



H OH 



^-D-glucopyranose 



CH2OH 



glucosan 



On the other hand /S-D-glucopyranose, under the same conditions, gives a 

 different anhydride, levoglucosan, resulting from the elimination of water 

 between the hydroxyl of C-1 and that of C-6, which is explicable from the 

 closeness of the two carbons in the formulae of Haworth. 



CH2OH 



H OH 



j8-D-glucopyranose 



H OH 



levoglucosan 



