LACTONE-STRUCTURE OF SUGARS 73 



CHO CH 2 (OH) 



I I 



CH(OH) CH(OH) 



CH(OH) CH(OH) 



+ H 2 



CH(OH) CH(OH) 



CH(OH) CH(OH) 



CH 2 (OH) CH 2 (OH) 



This view, which never had any experimental support, was rendered 

 unnecessary and untenable by the discovery of the fact that two 

 different forms of d-glucose are obtainable, isomers of one another 

 but differing in rotatory power. The one form, a-d-glucose, crystallizes 

 out at ordinary temperatures from seventy per cent, alcohol, and has 

 a molecular rotation of ()D + 110; the other, /3-d-glucose, crystal- 

 lises out from solutions in water at temperatures above 98 C., and 

 has a molecular rotation of ()D + 19. It appears that there are 

 indeed twostereo-isomeric forms of d-glucose, which would be impossible 

 were there onlv four asvmmetric carbon atoms in the molecule, as the 

 formula CHO - CH(OH) - CH(OH) - CH(OH) - CH(OH) - CH 2 (OH) 

 requires. The glucose molecule must, in fact, contain not less than 

 Five asymmetrical carbon atoms. This conclusion, first suggested by 

 Simon, was verified by Armstrong in the following way: 



Two methylated d-glucoses are known, formed from glucose by the 

 replacement of a hydrogen by a methyl group. The structures of these 

 two methyl glucosides are believed to be respectively: 



CH 3 O CH HC O CH 3 



HCOH \ HCOH N 



HOCH ' / HOCH 



HC/ HC 



HCOH H 



U' 



COH 



CH 2 OH CH 2 OH 



a-methyl-d -glucoside /3-methyl-d-glucoside 



Each of these glucosides can be hydrolyzed by an appropriate 

 ferment. Now it is observed that a glucose of high rotatory power is 

 produced in the hydrolysis of the a-methyl glucoside, while on adding 

 a drop of ammonia to the solution the rotation rapidly falls to the 

 equilibrium-value of the rotatory power of ordinary glucose. On the 

 other hand, when the 0-methyl glucoside is hydrolyzed, a glucose of 

 low rotatory power is produced, and on adding a drop of ammonia to 



