Equilibres conformationnels de glucides au niveau de liaisons σ sp²‐sp³ C‐C. III Dérivés d'oximes d'aldéhydo‐sucres utilisation de tris‐dipivaloylméthanato‐europium

A series of sugar oximes and O‐methyloximes of the general formula RCHNOR′ (R′  H, CH 3 ) have been studied by PMR. spectroscopy. These compounds exist in solution as a mixture of the syn and anti isomers. The conformational equilibrium of the syn isomers seems to consist exclusively of the eclipsed rotamers, whereas for the anti isomers there appears to be a significant contribution from bisecting rotamers. Using tris‐dipivaloylmethanato‐europium it is found that the α proton of the anti oximes is much more deshielded than the corresponding proton of the syn isomers, which means that the downfield shift of a particular proton does not depend exclusively on its distance from the oxygen of the oxyimino group.