CHO 



I 

 HO C H 



I 

 H C OH 



I 

 H C OH 



HO C H 



CH 2 OH 



1 galactose. 



CHO 

 HO C H 



HO C H 



I 

 HO C H 



HO C H 



CH 2 OH 



1-allose. 



57 



CHO 



HO C H 

 HO C H 



HO C H 



I 

 H C OH 



CH 2 OH 

 d-talose. 



CHO 



HO C H 



I 

 H C OH 



H C OH 



1 I 

 CH 2 OH 



d-altrose. 



The various sugars have been prepared synthetically and their con- 

 stitutional formulse confirmed. Thirteen of them are laboratory 

 products, and only three of them are met with in nature, to wit: 

 d- glucose, d- mannose and d- galactose. 



In addition to these hexoses of the aldehyde type, or Aldoses, another 

 hexose of quite a different type is of very common occurrence in nature, 

 namely fruit-sugar or Fructose. Unlike all of the hexoses considered 

 above, fructose is a sugar of the ketone type, or ketose. Its structure 

 may be represented by the formula : 



CH 2 OH 



CO 



HO C H 

 H C OH 

 H C OH 



CH 2 OH 



Fructose exists in a dextrorotatory and a levorotatory form, the 

 one being the mirror-image of the other. We customarily distinguish 

 between dextro- and levorotatory forms by the prefixes employed 

 above, d- and 1-; as, for example, d-glucose and 1-glucose. The 

 form of fructose which is represented in the formula given is the 

 levorotary form, but it is, nevertheless, termed d-fructose, because of 

 its close relationship to d-glucose, which will be apparent on comparing 

 the two f ormulse : 



