1914-15.] 
The Optical Rotation of Sugars. 
23 
The so-called y-oxidic constitution offers a reasonable explanation of the 
differences between the two forms of sugars — e.g., for glucose, 
HO . C . H 
H . C . OH 
/\ 
/\ 
/ \ 
/ \ 
H . C . OH \ 
H . 
, C . OH \ 
1 0 
and 
1 0 
HO . C . H / 
HO , 
. C . H / 
\ / 
\ / 
\/ 
\/ 
HC 
HC 
1 
1 
H . C . OH 
1 
H . C . OH 
i 
CH2OH 
CHgOH 
Of the theories advanced to explain the mechanism of the change from 
the a- to the modification, only one or two need be mentioned. The 
first, that of Lowry {Chem. Soc. J., 1903, Ixxxiii, 1314), supposes the y-oxidic 
ring to break up with formation of aldehydrol or aldehyde hydrate thus — 
HO 
C . H 
+11,0 
CH(OH), 
1 
-H^O 
H . C . OH 
1 - 
(0H0H)2 0 
^ 
(CH0H)2 
\ 

(CHOH)j 
1 
-HgO 
1 
-f-H20 
CH^^ 
CHOH 
CH-- 
1 
1 
CHOH 
1 
CHOH 
1 
CHOH 
1 
j 
CHgOH 
j 
CH 2 OH 
1 
CH 2 OH 
0 
the addition and splitting off of water taking place, so that both modifica- 
tions may be formed. 
The second, that of E. F. Armstrong {Chem. Soc. J., 1903, Ixxxiii, 1305), 
supposes the y-oxidic ring to remain unbroken, but that water becomes 
attached to the y-oxidic oxygen and thereafter is separated in different 
ways giving the a- and /3- forms respectively. The formation of an 
oxonium compound is possible, but problematical, in the case of the sugars 
{cf. Mackenzie, Sugars, pp. 128-131). 
Both these hypotheses assume the presence of water in the solution, and 
indeed the majority of the measurements of the mutarotation of sugars has 
been carried out in aqueous solution. Methyl and ethyl alcohols and 
acetone were not available as solvents owing to the very small solubility 
of most of the sugars in these liquids. Using mixtures of the alcohol or of 
acetone with water as solvent, the rate of mutarotation was diminished, 
an argument used in support of the theory that the mutarotation 
