Molécules modèles des motifs des poly-1,4-glucosides. II. Etude, par spectroscopie infrarouge, des conformations chélatées des diastéréoisomères modèles et discussion dans le cadre des chélations glucosidiques

We have made a systematic study of the infrared spectra, in the chelation region 3700-3300 cm −1 , of each of 30 separate diastereoisomers in dilute solution in carbon tetrachloride. Those diastereoisomers which have configurations corresponding to those of cellulose or amylose were examined more carefully. Depending on the structure of the model molecule and its diastereoisomeric configuration, it was possible to observe absorption bands corresponding to chelation in rings of 5, 6, 7 or 8 members. Most frequently the geometry of the chelated conformations varies from one diastereoisomer to another of a single molecule. The diastereoisomers of hydroxylated acetals have permitted the recognition of the result of a competition between two hydroxyl groups for the same proton accepting site. Discussion of these experimental results in terms of glucosidic chelations have led to the hypothesis that the chelations are in cellobiose, in methyl β-cellobioside and in cellulose, respectively. We have confirmed the chelation in the case of maltose, methyl β-maltoside and amylose and it seems reasonable to suggest that a chelation , can exist in these α-1,4-glucosides.[Journal translation]