205 
1915-16.] The Optical Rotation of Sugars. 
mutarotation is in any way dependent on internal changes undergone by 
such enolic forms. On the other hand, the recent recognition of the 
existence of glucose in the two forms termed collectively ‘ y-glucose ’ 
(Irvine, Fyfe, and Hogg, Trans. Ghem. Soc., 1915, cvii, 524) opens up the 
possibility that the phenomenon of mutarotation may involve these new 
varieties of sugars, so that detailed discussion of the results which follow 
may be deferred. 
Irvine and Steele have, however, discussed the mechanism of muta- 
rotation in aqueous solution in a paper {Ghem. Soc. J., 1915, cvii, 1230) 
published after the completion of the experimental work described below. 
On the evidence of measurements of the conductivities of certain methylated 
sugars in aqueous and in dilute boric acid solutions, they favour E. F. 
Armstrong’s oxonium theory of the mechanism of mutarotation in which 
the y-oxidic oxygen atom displays quadrivalency, a hydrogen atom and a 
hydroxyl group satisfying the two latent valencies. What effect boric 
acid has upon the /3- form of the sugars has not yet apparently been 
determined experimentally, but it is tacitly assumed that the /3- form would, 
under similar circumstances, arrive at the same equilibrium mixture as 
that attained by the a- form. 
The mutarotation of sugars has been most fully studied in the case 
of aqueous solutions, but measurements in pyridine solution have also 
been made, and now those in formamide solution are available. The last- 
mentioned solvent probably possesses the — NH 2 group, though it may 
NH 
be argued that formamide has an imino H . C 
\ 
OH 
and not the amide 
NH 2 
constitution H . C . The very low conductivity of the formamide 
\ 
O 
used in the following experiments makes it, on the whole, improbable 
that the imino modification was present. Now a definite compound of 
/3-glucose and pyridine is known, and, this being so, it is conceivable that 
the mechanism of mutarotation is due to the formation of such compound 
and subsequent splitting off of the pyridine molecule with formation of 
a- and /3- forms. Under certain conditions only the /3- form is actually 
formed. 
The authors, of whom one is on military duty and the other has 
returned to India, are unable at the present time to present a full 
theoretical discussion of the subject, and must content themselves with 
