Search results
Results From The WOW.Com Content Network
In chemistry, the Fischer projection, devised by Emil Fischer in 1891, is a two-dimensional representation of a three-dimensional organic molecule by projection. Fischer projections were originally proposed for the depiction of carbohydrates and used by chemists, particularly in organic chemistry and biochemistry .
The three bits, from left to right, indicate the position of the hydroxyls on carbons 4, 3, and 2, respectively: to the right if the bit value is 0, and to the left if the value is 1. The chemist Emil Fischer is said [ citation needed ] to have devised the following mnemonic device for remembering the order given above, which corresponds to the ...
The D/L system (named after Latin dexter and laevus, right and left), not to be confused with the d-and l-system, see above, does this by relating the molecule to glyceraldehyde. Glyceraldehyde is chiral itself and its two isomers are labeled D and L (typically typeset in small caps in published work).
The determination is made based on the chirality of the asymmetric carbon furthest from the aldehyde end, namely the second-last carbon in the chain. Aldoses with alcohol groups on the right of the Fischer projection are D-aldoses, and those with alcohols on the left are L-aldoses. D-aldoses are more common than L-aldoses in nature. [1]
For example, there are 16 distinct aldohexose stereoisomers, but the name "glucose" means a specific pair of mirror-image aldohexoses. In the Fischer projection, one of the two glucose isomers has the hydroxyl at left on C3, and at right on C4 and C5; while the other isomer has the reversed pattern.
The Fischer projection is a systematic way of drawing the skeletal formula of an open-chain monosaccharide so that each stereoisomer is uniquely identified. Two isomers whose molecules are mirror-images of each other are identified by prefixes ' D-' or ' L-', according to the handedness of the chiral carbon atom that is farthest from the carbonyl.
Nonetheless, the Fischer projection is a simple way of depicting multiple sequential stereocenters that does not require or imply any knowledge of actual conformation. A Fischer projection will restrict a 3-D molecule to 2-D, and therefore, there are limitations to changing the configuration of the chiral centers.
Glucose (before oxidization) The Fischer projections of D-glucose (left) and D-glucuronic acid (right). Glucose's terminal carbon's primary alcohol group has been oxidized to a carboxylic acid. Uronic acids (/ ʊ ˈ r ɒ n ɪ k /) or alduronic acids are a class of sugar acids with both carbonyl and carboxylic acid functional groups. [1]