Acyclic Sugars and Their Derivatives

The most useful way to depict the various conformational states of an acyclic sugar chain is by means of a formalized drawing that shows the relative dihedral angles of the substituents at each end of a carbon-carbon bond. Two such types of representation are the sawhorse and Newman (Boeseken) formulas, as illustrated for erythritol. The zigzag type of representation shown has the advantage that it can be employed to display the relative orientations of groups along a chain of several atoms that lie approximately in a plane (for example, the plane of the paper). 

The relationship between configuration and conformation observed for the unsubstituted alditols in the crystalline state can be used to predict, with significant confidence, the favored conformations of other acyclic sugar derivatives whose structures have not yet been determined experimentally. 

A conformational assignment from n.m.r. spectroscopy for an acyclic sugar chain in solution was reported in 1965. Analysis of the proton 

The importance of parallel 1,3-interactions in determining the favored conformational state of acyclic sugar derivatives in solution was also apparent from n.m.r.-spectral studies of polyhydroxyalkyl-quinoxalines in methyl sulfoxide, and of their acetates in carbon tetrachloride. 

The conformations of the peracetylated aldose diethyl dithioacetals in chloroform solution have been examined by n.m.r. spectroscopy, and the term sickle was introduced to designate the conformation generated from the extended, planar, zigzag form by rotation through 120° about an internal carbon-carbon bond. Such a sickle arrangement is adopted in solution by the D-xylose (8) and D-ribose (9) diethyl 

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