218 



A. T. RTXGEH AXI) EMIT. J. HAUMAXX 



the basis of this con figuration it is assumed that glucose may readily 

 behave like an aldehyde by breaking the y-oxido ring, thus: 



H 



HO C OH 



a carbon 

 (5 carbon 

 7 carbon 

 5 carbon 



C 



I |\H 



HCOII IICOH 



water | water | 



O ;r~ HOCII < -- - HOCII 

 water | + water | 



HCOII HCOH 



Closed ring or 

 Y-oxide form 



HCOH 



I 

 CH 2 OH 



Aldehydrol 



HCOH 



I 

 CH 2 OH 



Aldehyde 



An intermediate aldehyde-hydrate or aldehydrol form is believed to 

 result by hydrolysis, and from this in turn the aldehyde form originates. 

 The action is a reversible one, and it is assumed that when an agent that 

 will act upon the aldehyde group is added to an aqueous solution of glucose, 

 the small amount of aldehyde-hydrate present is acted upon, thereby dis- 

 turbing the equilibrium. A fresh quantity of the hydrate is formed and 

 so the process is kept up. 



Isomerism and Asymmetry. Bodies having the same elementary com- 

 position, but possessing different properties, are called isomers or isome- 



CH 3 \ 



rides. Thus ethyl alcohol CIL> and methyl ether O are isomers. 



I CH 3 / 



CH,OH 



Both have the empirical formula of C 2 H O. When, however, in addition 

 to having the same number of atoms of the same kind, these atoms are ar- 

 ranged iu the same general way, so that each compound has the same chemi- 

 cal groups, and consequently similar chemical properties, but the "space 

 relationships" of these groups within the molecule are different, such sub- 

 stances are said to be stereoisomeric. 



Sugars illustrate this form of isomerism especially well. For example, 

 glucose and galactose are both aldohexoses. They have the same empirical 

 formula) and the same chemical groups, but the space relationships or 

 configuration of these groups differ. 



These differences are illustrated in the following structural formulas : 



