28 



W. G. OVEREND AND M. STAGEY 



TABLE III 



Reaction op Tri-O-benzoyl-D-ribopyranosyl Hamdes with 



Dioxane-Methanol (1:9) at 20° 



Compound 



K X 10* Time of 



min., logio "half -change," 

 min. 



Final Wr 



"Calculated on the assumption that each halide was quantitatively converted to methyl pentoside 

 tri-0-benzoate. Methyl ^-d ribopyranoside 2,3,4-tri-O-benzoateshows lalo" — 65.2° in dioxane -methanol (1:9). 



to exist in a variety of tautomeric structures, since the Schiff base {syn- 

 or a7iti-io\m. of XXV) contains potentialities for isomerism and might 

 conceivably tautomerize to the anomeric pyranosides (XXVI and XXVII) 

 or the anomeric pair of furanosides (XXVIII and XXIX). These possible 

 changes have led to some confusion in explanations of the behavior of 

 A^-ribosides. 



RNH— C— H 



I 

 H— C— OH 



H— C— OH 



H— C— OH 



CH2— 0^ 

 XXVI 



NH2R 



CHO 



H— C— OH 



I 



I 

 H— C— OH 



H— C— OH 



CH2OH 

 XXIV 



H— C— NHR 



I 

 H— C— OH 



H— C— OH 



H— C— OH 



I 

 CH2 



-O^ 



XXVII 



