38 



CHEMISTRY OF PLANT LIFE 



2. Aldohexoses of the dulcitol series: 



d-Galactose 

 CH 2 OH 



H C OH 



J-Galactose 

 CH 2 OH 



HO C H 



I 



3. Ketohexoses: 



d-Fructose 

 CH 2 OH 



H C OH 

 H C OH 

 HO C H 

 C=0 

 CH 2 OH 



C 



H 2 OH 



CH 2 OH 



Reference will be made in subsequent paragraphs to the prob- 

 able chemical constitution of the monosaccharides other than 

 hexoses; but the above discussion of the structure of the hexoses 

 will serve as a sufficient introduction to the study of the compo- 

 sition of the common carbohydrates. 



CHARACTERISTIC REACTIONS OF HEXOSES 



Specific Rotatory Power. All soluble carbohydrates, since 

 they contain asymmetric carbon atoms, with the consequent 

 larger groups on one side of the molecule than the other, rotate 

 the plane of polarized light when it passes through a solution of 

 the carbohydrate in question. The amount of the rotation depends 

 upon the nature of the carbohydrate, the concentration of the 

 solution, and the length of the column of solution through which 

 the ray of polarized light passes. But the same definite amount 



