Equilibres conformationnels de glucides au niveau de liaisons s <i>sp²‐sp³</i> CC. II Dérivés d'hydrozones d'<i>aldéhydo</i>‐sucres

Abstract

Abstract A series of alkyl‐and aryl‐hydrazones of different types of aldehydo ‐ sugars with blocked hydroxy groups have been studied, mainly by PMR. spectroscopy. No traces of the azoalkane or ene‐hydrazine forms were detected; the hydrazones were found to exist only in the syn form, except for the cases where an intramolecular hydrogen bond between the ‘amino’ hydrogen of the hydazono group and an oxygen o the glycosyl group provides an extra‐stabilization to the anti isomer. Most of these syn hydrazones seem to exist as an equilibrium of the ‘classical’ eclipsed rotamers. The influence of solvent polarity both on configurational and conformational equilibria has been examined. The factors which determine the relative stability of the conformers about a sp 2 ‐ sp 3 s̀ bond, particularly some kind of non‐bonded attraction, are discussed.