CARBOS SOURCES 



119 



1. 



2. 



CHO 



H— C— OH 



3. HO— C— H 



I 



4. H— C— OH 



5. 

 6. 



H— C— OH 



I 



CHoOH 

 D-Glucose 



CHO 



I 

 HO— C— H 



I 

 H— C— OH 



I 



HO— C— H 



HO— C— H 



I 



CH.OH 

 L-Ghicosc 



The letters d and l indicate that these sugars belong to different series; 

 they do not indicate optical rotation. The small letters d and / have 

 been used in the past to express two separate ideas, optical rotation or 

 configuration. The use of d and I in the old literature makes it difficult 

 at times to discover which enantiomorph was meant. The configuration 

 of the secondary hydroxyl group farthest from the carbonyl group deter- 

 mines to which series a sugar belongs. D-Glucose is the form which 

 occurs naturally and is meant when glucose is used without qualification. 

 Not all naturally occurring sugars belong to the d series; e.g., L-arabinose. 

 For the sake of clearness and accuracy, the series designation should 

 always be used where there is any chance of confusion and misinterpre- 

 tation. Pigman and Goepp (1948) point out that only sugars of the 

 galactose type occur naturally as both enantiomorphs. D-Galactose is 

 fermented by some yeasts, while L-galactose is not. 



Hexoses. The following hexoses occur naturally: D-glucose, D-man- 

 nose, D-galactose, L-galactose, D-fructose, and L-sorbose. It is doubtful 

 if L-sorbose occurs in green plants, but it is formed from sorbitol by 

 bacterial {Acetobacter suboxydans) oxidation (Bertrand, 1904). 



CHO CHO CHoOH 



H— C— OH 



HO— C— H 



C=0 



