CONSTITUTION 



83 



is crystallized from 70 per cent alcoholic solution at ordinary 

 temperatures, a modification known as a-glucose is obtained 

 whose specific rotation is a^ = + 110°; if crystallized from 

 water at a temperature above 98°, another variety, known 

 as j8-glucose (a^ = + I9°), is obtained ; if either a-glucose 

 or jS-glucose is dissolved in water, a gradual change in rotation 

 is observed until a steady value of a^ = 52"5° is attained, 

 which is regarded as the specific rotation of an equilibrium 

 mixture of a- and j3-glucose. The attainment of the stable 

 condition is accelerated by acids, and is practically instan- 

 taneous in presence of traces of alkali. 



It will be readily understood that such a bridge or ring 

 structure as is represented by the y-lactone may also be de- 

 scribed as a butylene oxide formula, seeing that four carbon 

 atoms are involved in the ring. Theoretically isomeric sugars 

 possessing an ethylene, propylene, amylene, or hexylene oxide 

 formula should also be a possibility : — 



1 CHOH— , 



I o 



2 CH 1 



I 

 CHOH 



I 

 CHOH 



CHOH 



I 

 CH.,OH 



Ethylene oxide 



I CHOH— I 



CHOH O 



I I 

 3 CH 1 



CHOH 



I 

 CHOH 



I 

 CH2OH 



Propylene oxide 



I CHOH- 

 CHOH 

 CHOH O 

 CHOH 



5 CH 



CH2OH 

 Amylene oxide 



I CHOH- 



I 

 CHOH 



I 

 CHOH 



I 

 CHOH 



I 

 CHOH 



O 



6 CH2 



Hexylene oxide 



It has been the task of Irvine and his collaborators to 

 investigate this aspect of the isomerism of the sugars. Irvine's 

 resume * gives an account of these important investigations 

 which cannot be further considered here owing to exigencies 

 of space. The work of Irvine appeared to have firmly es- 

 tablished the butylene oxide formula for glucose, but in the 

 light of subsequent work the amylene oxide formula is now 

 generally accepted.f This implies the recognition of the fact 

 that glucose and the other hexoses are six-membercd hetero- 

 cyclic compounds whose constitution may be represented as 

 follows : — 



* Irvine : " J. Chem. Soc," 1923, 123, 898. 



t Charlton, Haworth, and Peat : id., 1926, 89, 1858. 



