CARBOHYDRATES 705 Mannose differs from glucose in configuration at C-2. All hydroxyl groups are equatorial in B-D-glucopyranose; the hydroxyl at C-2 is axial in B-D-mannopyranose (c) The conformational depiction of B-L-mannopyranose begins in the same way as that of B-D-mannopyranose. L-Mannose is the mirror image of D-mannose. CHO CHO CH,OH H 10-H H HH HO-H CHOH D-Mannose L-Mannose Eclipsed conformation To rewrite the eclipsed conformation of L-mannose in a way that permits hemiacetal forma tion between the carbonyl group and the C-5 hydroxyl, C-5 is rotated 120 in the clockwise HO CH,OH H te about CHOH CHOH H C-S bond Translating the Haworth formula into a proper conformational depiction requires that a choice be made between the two chair conformations shown H HO CH,OHH H H H HH OH OH HO CHOH OH H OH Haworth formula of Less stable chair conformation More stable chair confor B-L-mannopyranose ChOH is axial CH,OH is equatoria (d) The Fischer projection formula for L-ribose is the mirror image of that for D-ribose CHO CHO CH2OH H OHHO→H HO HO HOHO H-OH L-Ribose Eclipsed conformation of L-ribose is Haworth formula of Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE WebsiteMannose differs from glucose in configuration at C-2. All hydroxyl groups are equatorial in -D-glucopyranose; the hydroxyl at C-2 is axial in -D-mannopyranose. (c) The conformational depiction of -L-mannopyranose begins in the same way as that of -D-mannopyranose. L-Mannose is the mirror image of D-mannose. To rewrite the eclipsed conformation of L-mannose in a way that permits hemiacetal forma￾tion between the carbonyl group and the C-5 hydroxyl, C-5 is rotated 120° in the clockwise sense. Translating the Haworth formula into a proper conformational depiction requires that a choice be made between the two chair conformations shown. (d) The Fischer projection formula for L-ribose is the mirror image of that for D-ribose. CHO CH2OH H H H OH OH OH d-Ribose CHO CH2OH HO HO HO H H H l-Ribose Eclipsed conformation of l-ribose is oriented properly for ring closure. HO H HO H HO H CH2OH Haworth formula of -l-ribopyranose HO H HO H HO H H O OH C O H HO H H CH2OH HO H OH H H O OH Haworth formula of -l-mannopyranose Less stable chair conformation; CH2OH is axial OH H H CH2OH H H HO H OH OH O More stable chair conformation; CH2OH is equatorial OH OH OH H H H H HO HOCH2 O H HO H HO H HO H H OH CH2OH C H O O 1 3 2 4 5 5 6 HO H H CH2OH HO H H OH OH C H 1 3 2 4 -l-Mannopyranose (remember, the anomeric hydroxyl is down in the l series) HO H H CH2OH HO H H OH H OH O rotate about C-4 C-5 bond CHO CH2OH H HO H HO H OH H OH l-Mannose CHO CH2OH HO H OH H OH H HO H d-Mannose Eclipsed conformation of l-mannose HO H H H HO HO H OH CH2OH C O H CARBOHYDRATES 705 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website