194 THE CARBOHYDRATES. 



Gluconic acid = CH 2 (OH).[CH(OH)] 4 .COOH; 

 Saccharic acid=COOH.[CH(OH)] 4 .COOH. 



The monocarboxylic acids are easily transformed into their anhydrides 

 (lactones), and these latter are of special interest because, as shown by 

 FISCHER, they can be changed into the corresponding aldehyde, i.e., 

 the corresponding aldose, by nascent hydrogen. 



The monosaccharides are converted into the corresponding polyhydric 

 alcohols by nascent hydrogen. Thus ARABINOSE, which is a pentose, 

 CsHioOs, is transformed into the pentatomic alcohol, ARABITE, C 5 H 12 O5. 

 The three hexoses, DEXTROSE, LEVULOSE, and GALACTOSE, CeH^Oe, 

 are transformed into the corresponding three hexites, SORBITE, MANNITE, 

 and DULCITE, CeH^Oe- The ketoses, on the contrary, due to their 

 constitution, yield a mixture of two alcohols on the same treatment. 

 From d-levulose for example we obtain a mixture of d-sorbite and l- 

 mannite. On careful oxidation of the polyhydric alcohols the cor- 

 responding sugar can be prepared. 



Numerous isomers occur among the monosaccharides, and especially 

 in the hexose group. In certain cases, as, for instance, in glucose" and 

 levulose, we are dealing with a different constitution (aldoses and ketoses) , 

 but in most cases we have stereoisomerism due to the presence of asym- 

 metric carbon atoms. 



As the monosaccharides from the trioses upward contain asymmetric 

 carbon atoms they occur as optically active bodies in a 1-, d- , and racemic 

 form, r or d-l form, which is a combination of the first two forms. As 

 the number of asymmetric carbon atoms increases so does the number 

 of possible stereoisomeric forms enlarge. As the number according to 

 VAN'T HOFF is 2 n , where n represents the number of asymmetric 

 carbon atoms, then for the aldo-hexose, which contains 4 asymmetric 

 carbon atoms, 2 4 =16 stereo-chemically different forms can exist. In 

 fact, of these, 12 have been prepared and their geometric structure has 

 been explained and for which FISCHER has given configuration formulae. 



As these relations are readily conceived we will, for example, only 

 give the configuration formulas for the most important pentoses and 

 hexoses occurring in the animal body. 



COH COH COH COH 



HOCH HCOH HOCH HCOH 



HCOH HOCH HCOH HOCH 



HCOH HOCH HOCH HCOH 



CH 2 OH CH 2 OH CH 2 OH CH 2 OH 



d-Arabinose Z-Arabinose d-Xylose J-Xylose 



