84 THE CARBOHYDRATES 



H OH 



^/ OH OH 



J I* 



/I l\ 



H 



—OH o H / 



HO 



■HH— 



or 



, ._. -CH.OH HO\oH H / 



\ / \l !/ 



I 



> 



/\ H CHjOH 



H OH 



in which the reducing group is marked by a star and in which 

 the thickened hnes are all in the same plane : a discussion of 

 this question, together with some important deductions there- 

 from, is given by Haworth,* and in consequence the inter- 

 pretation of the constitution of all the polysaccharides and 

 glucosides derived from glucose has been modified. 



OXIDATION PRODUCTS OF SUGARS. 



Before proceeding to a description of the methods employed 

 for the identification of individual sugars, a brief consideration 

 of some of their products of oxidation is appropriate in view 

 of the fact that some are important constituents of natural 

 products. 



Oxidation by means of nitric acid under carefully controlled 

 conditions attacks both the terminal carbon atoms of alde- 

 hydic sugars,! leaving the intermediate secondary alcohol 

 groups unaltered. 



CH2OH— (CHOH)4— CHO->COOH— (CHOH)j— COOH 



In this way glucose, mannose, or galactose yield the di- 

 carboxylic acids saccharic, mannosaccharic, and mucic acids 

 respectively. 



An intermediate stage of oxidation, in which the aldehyde 

 group remains unaltered and only the terminal primary 

 alcohol group is oxidized to carboxyl, is represented by the 

 substances glucuronic and galacturonic acids of the formula 

 COOH . (CH0H)4 . CHO derived respectively from glucose and 

 galactose. 



* Haworth, " J. Soc. Chem. Ind.," 1927, 46, 295. 



+ Ketonic sugars are broken down to compounds containing fewer 

 carbon atoms. 



