702 CARBOHYDRATES (c) Again proceed by converting the Fischer projection into a three-dimensional representation CHO CHO HOCH,H HOCH, C-H Look at the drawing from a perspective that permits you to see the carbon chain oriented ver tically with the aldehyde at the top and the Ch,oh at the bottom. Both groups should point away from you. When examined from this perspective, the hydrogen is to the left and the hydroxyl to the right with both pointing toward you. CHO CHO HOCH, -C-H is equivalent to H-C-OH CHOH The molecule is D-glyceraldehyde 25. 2 Begin by drawing a perspective view of the molecular model shown in the problem. To view the compound as a Fischer projection, redraw it in an eclipsed conformation H OH H OH CH HOCH HOCH CHEO HO H taggered conformation Same molecule in eclipsed The eclipsed conformation shown, when oriented so that the aldehyde carbon is at the top, vertical bonds back, and horizontal bonds pointing outward from their stereogenic centers, is readily trans- formed into the Fischer projection of L-erythrose CHO HOH H is equivalent to HOC H, CHEO HO--H CHOH CHOH 25.3 L-Arabinose is the mirror image of D-arabinose, the structure of which is given in text Fig ure 25.2. The configuration at each stereogenic center of D-arabinose must be reversed to trans form it into L-arabinose CHO H H-OH HO-H oh Ho-h CHOH CHOH D-(-)-Arabinose L-(+)-Arabinose Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website702 CARBOHYDRATES (c) Again proceed by converting the Fischer projection into a three-dimensional representation. Look at the drawing from a perspective that permits you to see the carbon chain oriented ver￾tically with the aldehyde at the top and the CH2OH at the bottom. Both groups should point away from you. When examined from this perspective, the hydrogen is to the left and the hydroxyl to the right with both pointing toward you. The molecule is D-glyceraldehyde. 25.2 Begin by drawing a perspective view of the molecular model shown in the problem. To view the compound as a Fischer projection, redraw it in an eclipsed conformation. The eclipsed conformation shown, when oriented so that the aldehyde carbon is at the top, vertical bonds back, and horizontal bonds pointing outward from their stereogenic centers, is readily trans￾formed into the Fischer projection of L-erythrose. 25.3 L-Arabinose is the mirror image of D-arabinose, the structure of which is given in text Fig￾ure 25.2. The configuration at each stereogenic center of D-arabinose must be reversed to trans￾form it into L-arabinose. HO H H OH CHO H OH CH2OH d-()-Arabinose H HO HO H OH CHO H CH2OH l-()-Arabinose is equivalent to or CHO CH2OH HO C H HO C H L-Erythrose HO H HO H CHO CH2OH OH OH HOCH2 H H CH O OH H HOCH2 H HO CH O Staggered conformation Same molecule in eclipsed conformation OH OH HOCH2 H H CH O is equivalent to CHO CH2OH H OH C CHO OH HOCH2 C H is equivalent to CHO OH HOCH2 H CHO OH HOCH2 C H Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website