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FISCHER PROJECTION FORMULA
Of sugars, representations, by projection, of cyclic sugars, or derivatives thereof, in which the carbonchain is depicted vertically.
The lowest-numbered asymmetriccarbonatom (C-1 in aldoses; C-2 in 2-ketoses, e.g., fructose) is drawn at the top, and the rest of the carbon atoms of the chain are drawn in sequence adown the topcarbon atom.
For everycarbon atom, depicted in projection as lying in the plane of the paper, the carbon-to-carbon bond(s), which actually pointaway from the televiewer, are drawn as vertical lines. The left-hand and right-hand bonds of everycarbon atom, which actually point toward the televiewer, are, in projection, depicted as horizontal lines.
The conventions for the Fischer formulas of cyclic sugars are as follows: 1) if the highest-numbered asymmetriccarbonatom has its OH (or its replacement) lying to the right, as is the 2-OH of d-glyceraldehyde, the sugar has the d configuration; if the OH is to the left, the sugar has the l configuration. 2) On the anomeric carbonatom (C-1 in the aldoses; C-2 in the 2-ketoses), an OH or substituted OH that lies to the right, with the OH of the highest-numbered asymmetriccarbonatomalso to the right is defined to be a; if it is to the left, with the OH of the highest-numbered carbonatom still to the right, it is b; the reverse applies if the latter OH is to the left. 3) The orientation of a terminal CH2OH group in the aldoses carries no configurational significance, as it contains no asymmetriccarbon atom.