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Carbohydrates – Polyhydroxyaldehydes Or Polyhydroxy- Ketones of Formula (CH O) , Or Compounds That Can Be Hydrolyzed to Them

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Carbohydrates – Polyhydroxyaldehydes Or Polyhydroxy- Ketones of Formula (CH O) , Or Compounds That Can Be Hydrolyzed to Them Carbohydrates – polyhydroxyaldehydes or polyhydroxy- ketones of formula (CH2O)n, or compounds that can be hydrolyzed to them. (aka sugars or saccharides) Monosaccharides – carbohydrates that cannot be hydrolyzed to simpler carbohydrates; eg. Glucose or fructose. Disaccharides – carbohydrates that can be hydrolyzed into two monosaccharide units; eg. Sucrose, which is hydrolyzed into glucose and fructose. Oligosaccharides – carbohydrates that can be hydrolyzed into a few monosaccharide units. Polysaccharides – carbohydrates that are are polymeric sugars; eg Starch or cellulose. Aldose – polyhydroxyaldehyde, eg glucose Ketose – polyhydroxyketone, eg fructose Triose, tetrose, pentose, hexose, etc. – carbohydrates that contain three, four, five, six, etc. carbons per molecule (usually five or six); eg. Aldohexose, ketopentose, etc. Reducing sugar – a carbohydrate that is oxidized by Tollen’s, Fehling’s or Benedict’s solution. Tollen’s: Ag+ Ag (silver mirror) Fehling’s or Benedict’s: Cu3+ (blue) Cu2+ (red ppt) These are reactions of aldehydes and alpha-hydroxyketones. All monosaccharides (both aldoses and ketoses) and most* disaccharides are reducing sugars. *Sucrose (table sugar), a disaccharide, is not a reducing sugar. Glucose (a monosaccharide) Plants: photosynthesis chlorophyll 6 CO2 + 6 H2O C6H12O6 + 6 O2 sunlight (+)-glucose (+)-glucose starch or cellulose respiration C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy Animals plant starch (+)-glucose (+)-glucose glycogen glycogen (+)-glucose (+)-glucose fats or aminoacids respiration (+)-glucose + 6 O2 6 CO2 + 6 H2O + energy glyceraldehyde * CH2CHCH O an aldotriose OH OH CHO CHO H OH HO H CH2OH CH2OH D-(+)-glyceraldehyde L-(-)-glyceraldehyde D & L are used to relate configuration of the chiral center most removed from the reducing group ( C=O ). If the -OH is on the right in the Fischer projection, then it is D, if the -OH is on the left, then it is L aldotetroses * * CH2CHCHCH O OH OHOH CHO CHO H OH HO H H OH HO H CH OH CH2OH 2 D-erythrose L-erythrose CHO CHO H OH HO H HO H H OH CH2OH CH2OH L-threose D-threose * * * * (+)-glucose? An aldohexose CH2CHCHCHCHCH O Emil Fischer (1902) OH OHOHOHOH Four chiral centers, 24 = 16 stereoisomers CHO OH? CH2OH CHO CHO CHO CHO CHO CHO H OH HO H HO H H OH H OH HO H H OH HO H H OH HO H HO H H OH H OH HO H H OH HO H H OH HO H H OH HO H H OH HO H H OH HO H CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CHO CHO CHO CHO CHO CHO HO H H OH H OH HO H HO H H OH HO H H OH H OH HO H H OH HO H H OH HO H HO H H OH HO H H OH H OH HO H H OH HO H H OH HO H CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CHO CHO CHO CHO H OH HO H HO H H OH HO H H OH HO H H OH HO H H OH HO H H OH H OH HO H H OH HO H CH2OH CH2OH CH2OH CH2OH Ruff degradation – a series of reactions that removes the reducing carbon ( C=O ) from a sugar and decreases the number of chiral centers by one; used to relate configuration. CHO CO2H Br H OH 2 H OH H OH H OH H2O CH2OH CH2OH Ca2+ CO2 CHO H2O2 H OH H OH + H OH CH2OH Fe3 CH2OH D-(+)-glyceraldehyde Kiliani-Fischer synthesis. A series of reactions that extends the carbon chain in a carbohydrate by one carbon and one chiral center. C N C N COOH COOH CHO HCN H OH HO H + + H ,H2O H OH HO H H OH H OH H OH H OH H OH CH2OH CH2OH CH2OH CH2OH CH2OH diastereomers separable CHO O C H OH Na(Hg) H OH H OH H OH CH OH 2 H2C O -H2O lactone Epimers – stereoisomers that differ only in configuration about one chiral center. CHO CHO H OH HO H HO H HO H H OH H OH H OH H OH CH2OH CH2OH D-glucose D-mannose epimers CHO H OH HO H H OH H OH Exists only in solution. There are two solids: CH2OH o (+)-glucose α-glucose m 146 [α] = +112.2 β-glucose m 150o [α] = +17.5 In water each mutarotates to an equilibrium with [α] = +52.7 (63.6% β / 36.4% α) CHO OH OH H H OH H H O H O HO HO H HO HO H HO OH H OH H OH H OH H OH H OH H H CH2OH alpha-(+)-glucose beta-(+)-glucose CH OH 2 CH2OH O H H H O OH OH H OH H OH OH OH H H OH H OH Addition of alcohols to aldehydes/ketones: O OH OR' C + R'OH R C H R C H R H OR' OR' hemiacetal acetal geminal geminal ether/alcohol diether reducing! non-reducing! CHO OH OH H H OH H H O H O HO HO H HO HO OH HO H H OH H OH H OH H H H OH H OH CH2OH nucleophilic addition of -OH on carbon 5 to the aldehyde functional group HOH CHO H O CH O HO H OH HO H H OH H OH HO H H OH HO H α H OH H OH H OH HOH2C H HOH CH OH 2 OH H O HO HO OH β rotate C-5 OH to rear H OH H H HOH HOH H O H O HO HO HO H HO OH H OH H OH H OH H H alpha hemiacetal beta O D-glucopyranoses 4H-Pyran H H H OH HOHO O HO O HO H HO HO H H OH H H H OH H OH alpha furanose form beta furanose form D-glucofuranoses O furan HOH HOH H O H O HO HO HO H HO OH H OH H OH H OH H H alpha beta anomers - epimers at C-1 chair conformations - alpha has one group axial beta has all groups equatorial mutarotation in solution to 63.6% beta/36.4% alpha CH2OH O CH OH OH CH2OHO 2 HO H CH2OHO H OH H OH H OH H OH H OH H CH2OH OH H OH H CH2OH alpha-D-fructofuranose D-fructose beta-D-fructofuranose acetal OH H HOH H O CH3OH H HO O HO OH HO H HCl HO OCH3 OH H OH H H H H methyl beta-D-glucoside (glucoside - glucose acetal) non-reducing, does not muta- rotate Disaccharides: (+)-maltose “malt sugar” two glucose units (alpha) (+)-cellobiose two glucose units (beta) (+)-lactose “milk sugar” galactose & glucose (+)-sucrose “table sugar” glucose & fructose HOH H O HO two glucose units HO H OH H OH H alpha C-1 to C-4 H H O O HO OH H OH H H (+)-maltose reducing sugar HOH HOH H O HO H O two glucose units HO O H OH HO OH beta C-1 to C-4 H H H OH H H (+)-cellobiose reducing sugar HOOH HOH galactose beta C-1 H O H H O to C-4 glucose HO O H OH HO OH H H H OH H H (+)-lactose reducing sugar HOH H O H O HO 2 HO H H H C glucose alpha C-1 OH H H O to beta C1 fructose O H OH CH OH acetal 2 non-reducing HO H (+)-sucrose Polysaccharides starch cellulose Starch 20% amylose (water soluble) 80% amylopectin (water insoluble) amylose + H2O (+)-maltose (+)-maltose + H2O (+)-glucose starch is a poly glucose (alpha-glucoside to C-4) O O O O O O O O O O O O O O O O Amylopectin + H2O (+)-maltose (+)-maltose + H2O (+)-glucose Also a polyglucose, but branched every 20-25 units: O O O O O O O O O O O O CH2 O O O O O O O O O O O O O O O O Cellulose is a polyglucose with a beta-linkage: O O O O O O O O O O O O O O O O.
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