Open chain carbohydrates, conformation

Depiction of the Conformation of Open Chain Carbohydrates The Newman Projection... 

Open-chain carbohydrate derivatives are ideal objects for conformational analysis by H -NMR solution spectroscopy. The OH-proton signals are well separated from CH-methine proton signals, and decoupling experiments allow easy signal assignments. Polar carbohydrate derivatives and the carbohydrates themselves are soluble in dimethyl sulfoxide (DMSO), which destroys all inter-... 

Figure 4.2.6 Two effects determine the configurations of open-chain carbohydrate derivatives (a) gauche confirmations are favored in 1,2-diols over anti conformations, and (b) 1,3-syn diaxial interactions between hydroxyl substituents are repulsive and often lead to distortions of the all-anti chain.

Let us now look at molecules with two stereogenic centres, usually adjacent, which have two common substituents. The names of the two configurations are taken from two carbohydrates, but are now used quite generally. D-Erythrose shown in Fischer 11 and sawhorse 12 projections in its open-chain forms is such a compound. In 12 the pairs of like substituents are shown in an eclipsed conformation. 

---