15597.ch24_423-43810/20/054:54 M Page432 432 chapter 24 CARBOHYDRATES:POLYFUNCTIONAL COMPOUNDS IN NATURE HOHO HO OF -0 a-D-Xylopyrano CH3 CH H:C CH OH 0 B-D-Lyxopyranose 46.(i)The sugar has seven carbons and is a ketose.because HIOa treatr produces a mole of CO2 (ii)Because the sugar forms the same osazone as an aldose,its ketone must be at C2.So far.therefore.you have the following partial structure: CH2OH C=0 CHOH CHOH Stereochemistry unknown HOH」 -OH CH2OH (iii)and (v)tell you that CHO CHOH CHO CHOH CHOH CHOH CHOH CHOH H-C-OH H-C-OHThe best xylose and lyxose can do is have only one pair of adjacent cis hydroxy groups, so these readily form only monoacetals. 46. (i) The sugar has seven carbons and is a ketose, because HIO4 treatment produces a mole of CO2 (see a similar reaction of D-fructose, Section 24-5). The sugar has two CH2OH groups (leading to two formaldehydes) and four CHOH groups (leading to 4 mol of formic acid). (ii) Because the sugar forms the same osazone as an aldose, its ketone must be at C2. So far, therefore, you have the following partial structure: (iii) and (v) tell you that CHO CH2OH Aldoheptose A CHOH CHOH CHOH CHOH C OH Ruff Ruff H CH2OH Aldohexose B CHOH CHO CHOH CHOH H C OH CH2OH CH2OH C O CHOH Stereochemistry unknown CHOH CHOH H C OH D-sugar O HO HO OH OH CH3COCH3, H
-D-Lyxopyranose O HO HO O O CH3 H3C HO O HO HO OH HO O HO O O CH3 CH3 CH3COCH3, H -D-Xylopyranose 432 • Chapter 24 CARBOHYDRATES: POLYFUNCTIONAL COMPOUNDS IN NATURE 1559T_ch24_423-438 10/20/05 4:54 AM Page 432