Monosaccharides boat form

There are two possible types of strainless six-member pyranose rings, the boat (B) and the chair (C) forms and of these, the chair is usually preferred as there are fewer interactions across the ring between snbstituents. The rings can be defined as " 1 if C4 is above the plane (described by C2, C3, C5 and 05) and Cl is below it, or as C4 for the alternative ring. P-D-Glncopyranose has all substituents (OH) that are equatorial in the " 01 conformation, a possible reason why D-Glc is a common monosaccharide in nature. 

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