Fischer Projections

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Fischer Projection representation of a 3D molecule as a flat structure where a tetrahedral carbon is represented as two crossed lines. vertical line is going back behind of the plane of the page carbon C substituent horizonal line is coming out of the plane of the page CHO HOH2C OH H H CHO OH CH2OH H CHO OH CH2OH Fischer projection (R)-(+)-glyceraldehyde Manipulation of Fischer Projections: 1. Fischer Projection can be rotated by 180 ° only! CHO H OH CH2OH (R)-(+)-glyceraldehyde Rotation by 90
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  Fischer Projection representation of a 3D molecule as a flat structure where a tetrahedral carbon is represented as two crossedlines. Ccarbonsubstituenthorizonal line is coming outof the plane of the pagevertical line is going back behindof the plane of the pageHOH 2 CCHOHOH(R)-(+)-glyceraldehydeCHOCH 2 OHOHHCHOCH 2 OHOHHFischer projection Manipulation of Fischer Projections:1. Fischer Projection can be rotated by 180 ° only! (R)-(+)-glyceraldehydeCHOCH 2 OHOHHCH 2 OHCHOHHO180 ° rotationstill(R)-(+)-glyceraldehyde Rotation by 90 ° or -90 ° (270 °) invert the stereochemistry (R)-(+)-glyceraldehydeCHOCH 2 OHOHH90 ° rotationHOHCHOHOH 2 CCHOCH 2 OHOHHHOHCHOHOH 2 C(S)-(-)-glyceraldehydeThese two compounds are enantiomers Because of the convention of theFischer Projection (i.e., thevertical lines are going back andthe horizonal lines are comingforward) the 90° rotated Fisherprojection is actually theenantiomer of the srcinal  2. If one group of the Fischer projection is held steady, the other groups can be rotated either clockwise orcounter clockwise. (R)-(+)-glyceraldehydestill(R)-(+)-glyceraldehydeCHOCH 2 OHOHHhold this group steadyCHOOHHHOH 2 C Assigning R and S-configurations to Fischer projections1.Assign priorities to the four substituents according to the Cahn-Ingold-Prelog convention.2.Perform the two allowed manipulations of the Fischer projection to place the lowest priority group onone of the vertical positions (either top or bottom)3.If the priorities of the other three groups (1-2-3) proceed clockwise, the stereogenic center is assignedas R. If the priorities of the other three groups (1-2-3) proceed counter clockwise, the stereogeniccenter is assigned as S. CHOCH 2 OHOHH1234lowest prioritygroup. Move toa vertical positionHCH 2 OHCHOHO1342hold one groupsteady and rotatethe other threeThe priorities of the other threegroups (1-2-3) is clockwise. Thestereogenic center is assign as Rholdsteady  For more structures with more than one stereogenic center such as carbohydrates, the tetrahedral carbonsare stacked on top of one another. HHOOHOOHThreoseCHOHOHHOCH 2 OHH For carbohydrates, the convention is to put the carbonyl group at the top for aldoses and closest to the topfor ketoses. The carbons are numbered from top to bottom. HCHOOHHHOOHHOHHCH 2 OHCH 2 OHOHHOOHHOHHCH 2 OHD-GlucoseD-Fructose112 Carbohydrates and amino acids are designated as D- or L- according to the stereochemistry of the highestnumbered carbon in the Fischer projection. If the hydroxyl group (or amino group for amino acids) ispointing to the right in the Fischer Projection, the sugar (or amino acid) is designated as D. If thehydroxyl group (or amino group for amino acids) is pointing to the left in the Fischer projection, the sugar(or amino acid) is designated as L. Most naturally occurring carbohydrates are of the D-configurationwhile most naturally occurring amino acids are L. HCHOOHHHOOHHOHHCH 2 OHD-Glucose1CHOOHHHHOHHOCH 2 OHL-Arabinose1highest numberedstereogenic carbonhighest numberedstereogenic carbon234564532  Converting Fischer Projections into Haworth Projections.1.Identify the hydroxyl group which is cyclizing onto the carbonyl group. This hydroxy will become thering oxygen in the hemiacetal or hemiketal form of the carbohydrate. For D-glucose, it is the C5hydroxyl in the pyranose form; for D-ribose, it is the C4-hydroxyl for the furanose form.2.Manipulate the Fischer projection so this hydroxyl group is on the bottom.3.Draw the Haworth projection so that the ring oxygen is on the top. For pyranoses, draw the six-membered ring laying on it side with a oxygen at the upper right.4.Substituents on the right side of the Fischer projection will be on the bottom face of the Haworthprojection. Substituents on the left side of the Fischer projection will be on the top face of theHaworth projection.5.Remember that in the cyclic form, the C1-hydroxyl group (the anomeric center) can usually adopteither the up or down configuration. HCHOOHHHOOHHOHHCH 2 OHHCHOOHHHOOHHHHOH 2 COH D-glucose RingoxygenTOBTBTBBTTBTBTBBBTTOPyranoseFuranoseT= topB= bottomOOHOHCH 2 OHOHOH1123456 β -D-glucopyranoseCHOOHHOHHOHHCH 2 OHCHOOHHOHHHHOH 2 COH D-Ribose Ringoxygen1OHOHOHOHO β -D-ribofuranose12346
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