180 CARBOHYDRATES 



Many members of the group of carbohydrates have been prepared. 

 They may be conveniently divided into the following classes : 



I. Monosaccharoses. This class includes compounds containing 

 from 2, e.g., biose, CHO.CH 2 OH, to 9 carbon atoms e.g., nonose, 

 CHO.(CHOH) 7 .CH 2 OH. The members of interest from the present 

 standpoint are those containing 5 or 6 carbon atoms, i.e., the pentoses 

 and hexoses. 



In the following list of these two groups, those members which 

 are of importance as occurring in plants are printed in black type. 

 The others have been prepared artificially. 



H \ 



(a) Aldoses, i.e., compounds containing the group \G 



CT 

 Pentoses, C S H 10 O 5 , 1-arabinose, CHO.(CHOH) 3 .CH 2 OH 



d-arabinose ,, 



1-xylose ,, 



^-xylose ,, 



Z-ribose ,, 



d-lyxose ,, 



Hexoses, C 6 H 12 O fi , d-glucose, CHO.(CHOH) 4 .CH 2 OH 



Z-glucose ,, 



d-mannose 



Z-mannose ,, 



d-galactose 



Z-galactose ,, 



d-gulose ,, 



Z-gulose ,, 



d-idose 



Z-idose , , 



cZ-talose ,, 



Z-talose ,, 



(b) Ketoses, i.e., compounds containing the group O = C<^ 



Pentose, Z-arabinulose, CH 2 OH.CO.(CHOH).,.CH l ,OH 

 Hexoses, d-fructose, CH.,OH.CO.(CHOH) 3 .CH,OH 



/-fructose ,, 



d-sorbose ,, , 



Z-sorbose ,, 



d-tagatose ,, 



The prefixes laevo-(Z-) and dextro-(^-), originally used to indicate the 

 direction of rotation of the plane of polarised light by solutions of the 

 various sugars, are now, by Fischer, employed to indicate the configu- 

 rations assigned to their constitutional formulae, and in the hexoses, 

 are descriptive of the position of the hydrogen atom attached to the 

 third carbon atom. 



Thus 



