THE CARBOHYDRATES AND THEIR METABOLISM 231 



Conversion of Glucose into Fructose and Mannose. In the presence 

 of alkalis, aqueous solutions of glucose, mannose and fructose are con- 

 verted into one another; slowly at room temperature, more quickly and 

 with some decomposition at higher temperatures. These most interesting 

 and important reactions were first observed by Lobry de Bniyn and A. 

 Van Ekenstein, 1902-1003. They noticed that if glucose were treated 

 with weak alkali at room temperature, the specific rotation changed from 

 + 52.5 to about 0. After standing several days or weeks, mannose and 

 fructose, as well as glucose, could be isolated from the solution. The 

 mechanism of the process was explained by Wohl. It will be remembered 

 that except for the terminal and a-carbon atoms, the space configuration 

 of glucose, fructose and rnannose is the same. The hydrogen atom at- 

 tached to the a-carbon in glucose and mannose "swings" from its position 

 to give rise to the common enol form. In the case of fructose the swing- 

 ing H atom is attached to the terminal C atom. The enol form is then 

 converted into all three of the possible hexoses. 



CHO 



HCOH 



HOCH 



HCOH 



HCOH 



CH 2 OH 



Glucose 



CHOII 



HOCH 



HCOH 



I 

 HCOH 



I 

 CH 2 OH 



Fructose 



CHO 



HOCH 



HOCH 

 HCOH 

 HCOH 



CH 2 OH 

 Mannose 



