Pentitols conformation

These results suggest that in the pentitols and hexitols, at least, the intermolecular H-bonds have only a secondary influence on the shape of the molecules in the solid state. The observed conformations in the solid state can be rationalized (16) in terms of the intramolecular interactions between hydroxyls which are believed to involve energies of the order of several kilocalories (27) (the interpretation of the NMR spectra of acetylated acyclic sugar derivatives in solution is based on the same type of hypothesis (29)). 

Xylitol 3 is a non-chiral, all-t/zreo-configured pentitol which allows grouping of all its hydroxyl functions on the same side of the C5 chain with a zigzag conformation. In the dinuclear cobalt(III) complex 25 (O Fig. 5) two entirely deprotonated zigzag conformers provide a proper Oio set of an edge-shared C02O10 dioctahedron, whereas in the similar diferrate(III) 16 (O Fig. 3) with the smaller aW-threo configured L-threitol, two hydroxyls are required to complete the dioctahedron [36]. 

Fourier Transform n.m.r. at 90 MHz has been used to probe the conformations o per-acetylated L-arabinononitrile, D-mannononitrile, D-glucononitrile, D-galactononitrile, 6-deoxy-L-galactononitrile, 2-deoxy-D-amhino-hexononitrile, and 2-deoxy-D-/yxo-hexononitrile. Zig-zag conformations were adopted for all except D-glucononitrile, which exists in the sickle form. Conformational studies on the four 1-amino-l-deoxy-D-pentitols and their hydrochlorides by 250 MHz H n.m.r. in D2O have shown that the D-arabino- and the D-lyxo-isomers adopt the extended zig-zag conformation, whereas the D-xylo- and D-nho-isomers, which have unfavourable 1,3-interactions, adopt the non-planar sickle conformation the results are similar to those obtained by J f-ray crystallo-... 

By means of specifically deuteriated derivatives, the n.m.r. of all pentitols and hexitols in water and their acetates in chloroform have been assigned. Qualitative correlations between chemical shift, configuration, and preponderant conformation were made, leading to practical empirical rules. ... 

Barker et have also studied the deamination of 1-amino-1-deoxy-pentitols and -hexitols. Tetrahydrofuran derivatives as well as pentitols and hexitols were the products. In deaminations, the ground-state conformation was thought to be a more important factor in product formation. 

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