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3.2.1.1.2.4 Pyranose and furanose ring structures
Alcohols react with the carbonyl groups of aldehydes and ketones to form hemiacetals and hemiketals respectively. The hydroxyl and either the aldehyde or the ketone groups of monosaccharides can likewise react intramolecularly to form cyclic hemiacetals and hemiketals.
The configurations of the substitutes of each carbon atom in these sugar rings are conveniently represented by their Haworth's Projection, in which the heavier ring bond project in front of the plane of the paper and the lighter ring bonds project behind it.
A sugar with a six-member ring is known as a pyranose in analogy with pyran, the simplest compound containing such a ring. Similarly, sugars with five-member rings are furanoses in analogy with furan.
Glucose and fructose form pyranose and furanose ring structures. Other pentoses and ketoses may also show ring structures. Ring structures of sugars presented are the most stable structures present in natural compounds. |