Sugars cyclic hemiacetals, conformation

Some of the most important saturated oxygen heterocycles are the sugars. Glucose is a cyclic hemiacetal—a pentasubstituted tetrahydropyran if you like—whose major conformation in solution is shown on the right. 

Many of the stereoelectronic effects in the list above govern reactivity, but the next section will deal with how stereoelectronic effects affect structure—and in particular conformation. Some of the most important saturated oxygen heterocycles are the sugars. Glucose is a cyclic hemiacetal—a pentasubstituted tetrahydropyran if you like—whose major conformation in solution is shown below. About two-thirds of glucose in solution exists as this stereoisomer, but hemiacetal formation and cleavage is rapid, and this is in equilibrium with a further one-third that carries the hemiacetal hydroxyl group axial (<1% is in the open-chain form). 

Draw the most stable conformation of the most stable cyclic hemiacetal form of this sugar, and give the structure a complete systematic name. 

In reality, the cyclic hemiacetal forms of sugars and their derivatives may assume a wealth of different ring conformations. For purposes of nomenclature, however, linear Fischer Projections and Haworth Representations with their quasi conformation-averaging planar-cyclic habit are best suited to illustrate the manifold stereochemicd relationships significant for carbohydrates. 

Glycosides of 3-deoxy-3-nitroaldoses are readily available by the cyclization of sugar dialdehydes with nitromethane. Introduced in 1958 by Baer and Fischer,48 the method has been widely employed, and some aspects have been reviewed.49,50 The term sugar dialdehydes refers to products of glycol cleavage of glycosides.51 The formation, structure, conformation, and reaction of such dialdehydes have been discussed in detail in previous Chapters of these Volumes.52-54 The compounds exist in aqueous and alcoholic solutions as solvated, cyclic forms that are internal hemialdals or hemiacetals.54 However, under the conditions of the nitromethane cyclization, mobile equilibria are rapidly shifted from such cyclic products toward carbonyl species, and it is, therefore, permissible and customary in... 

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