CARBOHYDRATES 715 25.21 Begin the problem by converting the Fischer projection of D-ribose to a perspective view. Remem ber that the horizontal lines of a Fischer projection represent bonds coming toward you, and the ver tical lines are going away from you H OH H OH is equivalent to HAOH H-OH CHOH CHOH Rank the groups attached to each stereogenic center. Identify each stereogenic center as either R or S according to the methods described in Chapter 7. Remember that the proper orientation of the low est ranked group(usually H)is away from you. Molecular models will be helpful here. Each of the stereogenic centers in D-ribose has the R configuration. The IUPAC name of D-ribose is(2R, 3R, 4R)- 2, 3, 4,5-tetrahydroxypentanal CHEO HC-2 is R H-OH CH,- is R 25.22 (a) The L sugars have the hydroxyl group to the left at the highest numbered stereogenic center in their Fischer projection. The L sugars are the ones in Problem 2520a and c CHO HO-H OH HOCH COH HO→H HO-H CHOH H H,C--OH-Highest numbered H3C HO CHOH (b) Deoxy sugars are those that lack an oxygen substituent on one of the carbons in the main hain. The carbohydrate in Problem 2520b is a deoxy sugar. CHO CHOH H-OH H-OH H H-L-H Nob d cs H CHOH Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website25.21 Begin the problem by converting the Fischer projection of D-ribose to a perspective view. Remem￾ber that the horizontal lines of a Fischer projection represent bonds coming toward you, and the ver￾tical lines are going away from you. Rank the groups attached to each stereogenic center. Identify each stereogenic center as either R or S according to the methods described in Chapter 7. Remember that the proper orientation of the low￾est ranked group (usually H) is away from you. Molecular models will be helpful here. Each of the stereogenic centers in D-ribose has the R configuration. The IUPAC name of D-ribose is (2R,3R,4R)- 2,3,4,5-tetrahydroxypentanal. 25.22 (a) The L sugars have the hydroxyl group to the left at the highest numbered stereogenic center in their Fischer projection. The L sugars are the ones in Problem 25.20a and c. (b) Deoxy sugars are those that lack an oxygen substituent on one of the carbons in the main chain. The carbohydrate in Problem 25.20b is a deoxy sugar. H H H OH OH CHO H H OH CH2OH No hydroxyl group at C-5 H CH2OH OH H H H H H HO OH O OH H3C OH CHO CH2OH H HO H Highest numbered H3C stereogenic center is l. OH HO HO HO O OH HOCH2 HO O OH OH H H OH CHO CH2OH H HO HO HO H Highest numbered stereogenic center is l. H H H OH OH CH OH CH2OH O C-2 is R C-3 is R C-4 is R H H H OH OH CH OH CH2OH O H H H OH OH CH OH CH2OH O is equivalent to CARBOHYDRATES 715 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website