Carbohydrates Classification of Carbohydrates monosaccharide disaccharide oligosaccharide polysaccharide Monosaccharide is not cleaved to a simpler carbohydrate on hydrolysis glucose, for example, is a monosaccharide Disaccharide is cleaved to two monosaccharides on hydrolysis these two monosaccharides may be the same or different C12H22O11 + H2O C6H12O6 + C6H12O6 glucose sucrose (a monosaccharide) fructose (a disaccharide) (a monosaccharide) Higher Saccharides oligosaccharide: gives two or more monosaccharide units on hydrolysis is homogeneous—all molecules of a particular oligosaccharide are the same, including chain length polysaccharide: yields "many" monosaccharide units on hydrolysis mixtures of the same polysaccharide differing only in chain length Some Classes of Carbohydrates No. of carbons Aldose Ketose 4 Aldotetrose Ketotetrose 5 Aldopentose Ketopentose 6 Aldohexose Ketopentose 7 Aldoheptose Ketoheptose 8 Aldooctose Ketooctose Fischer Projections and D-L Notation Fischer Projections Fischer Projections Fischer Projections of Enantiomers Enantiomers of Glyceraldehyde CH O CH O H OH HO H D L CH2OH CH2OH (+)-Glyceraldehyde (–)-Glyceraldehyde The Aldotetroses An Aldotetrose 1 CH O 2 H OH 3 H OH D 4 CH2OH stereochemistry assigned on basis of whether configuration of highest-numbered stereogenic center is analogous to D or L-glyceraldehyde An Aldotetrose 1 CH O 2 H OH 3 H OH 4 CH2OH D-Erythrose The Four Aldotetroses CH O CH O H OH HO H D-Erythrose and L-erythrose are H OH HO H enantiomers CH2OH CH2OH D-Erythrose L-Erythrose The Four Aldotetroses CH O CH O D-Erythrose and H OH HO H D-threose are diastereomers H OH H OH CH2OH CH2OH D-Erythrose D-Threose The Four Aldotetroses CH O CH O L-Erythrose and HO H HO H D-threose are diastereomers HO H H OH CH2OH CH2OH L-Erythrose D-Threose The Four Aldotetroses CH O CH O D-Threose and H H OH L-threose are HO enantiomers H OH HO H CH2OH CH2OH D-Threose L-Threose The Four Aldotetroses CH O CH O CH O CH O H OH HO H HO H H OH H OH HO H H OHHO H CH2OH CH2OH CH2OH CH2OH D-Erythrose L-Erythrose D-Threose L-Threose Aldopentoses and Aldohexoses The Aldopentoses There are 8 aldopentoses. Four belong to the D-series; four belong to the L-series. Their names are ribose, arabinose, xylose, and lyxose. The Four D-Aldopentoses CH O CH O CH O CH O H OH HO H H OH HO H H OH H OH HO H HO H H OH H OH H OH H OH CH2OH CH2OH CH2OH CH2OH D-Ribose D-Arabinose D-Xylose D-Lyxose Aldohexoses There are 16 aldopentoses. 8 belong to the D-series; 8 belong to the L- series. A Mnemonic for Carbohydrate Configurations The Eight D-Aldohexoses CH O H OH CH2OH The Eight D-Aldohexoses All CH O Altruists Gladly Make Gum In H OH Gallon CH2OH Tanks The Eight D-Aldohexoses All Allose CH O Altruists Altrose Gladly Glucose Make Mannose Gum Gulose In Idose H OH Gallon Galactose CH2OH Tanks Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose Gulose Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose H OH Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose HO H Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose H OH Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose HO H Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose H OH Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose H OH Mannose H OH Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose HO H Mannose H OH Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose HO H Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose H OH Mannose HO H Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose HO H Mannose HO H Gulose H OH Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose H OH Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose H OH Mannose H OH Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose HO H Mannose H OH Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose Mannose HO H Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose H OH Mannose HO H Gulose HO H Idose H OH Galactose CH2OH Talose The Eight D-Aldohexoses Allose CH O Altrose Glucose HO H Mannose HO H Gulose HO H Idose H OH Galactose CH2OH Talose L-Aldohexoses There are 8 CH O CH O aldohexoses of the L-series. H OH HO H They have the HO H H OH same name as H OH HO H their mirror image except the prefix is H OH HO H L- rather than D-. CH2OH CH2OH D-(+)-Glucose L-(–)-Glucose Cyclic Forms of Carbohydrates: Furanose Forms R R •• •• • C O• + R"OH R"O C O H •• •• •• R' R' Product is a hemiacetal. Cyclic Hemiacetals R R OH C O C OH O Aldehydes and ketones that contain an OH group elsewhere in the molecule can undergo intramolecular hemiacetal formation. The equilibrium favors the cyclic hemiacetal if the ring is 5- or 6-membered. Carbohydrates Form Cyclic Hemiacetals 1 CH O 2 OH O 4 1 3 3 2 H 4 CH2OH equilibrium lies far to the right cyclic hemiacetals that have 5-membered rings are called furanose forms D-Erythrose 1 CH O 2 H H OH H H OH O 4 1 3 H OH H H 3 2 4 OH OH CH2OH stereochemistry is maintained during cyclic hemiacetal formation D-Erythrose 1 2 4 1 turn 90° 3 3 2 4 D-Erythrose move O into 1 position by rotating 4 about bond 2 between carbon-3 3 and carbon-4 D-Erythrose 1 4 1 4 3 2 3 2 D-Erythrose 1 close ring by 4 hemiacetal formation 3 2 between OH at C-4 and carbonyl group D-Erythrose 1 1 4 4 3 2 3 2 D-Erythrose anomeric carbon 1 CH O 2 H H OH H H OH O 4 1 3 H OH H H 3 2 4 OH OH CH2OH stereochemistry is variable at anomeric carbon; two diastereomers are formed D-Erythrose H H H H H H H OH O O 4 1 4 1 OH H H 3 2 H 3 2 OH OH OH OH α-D-Erythrofuranose β-D-Erythrofuranose D-Ribose 1 CH O 2 H OH H 3 OH H 4 OH 5 CH2OH furanose ring formation involves OH group at C-4 D-Ribose 1 CH O 5 2 CH OH H OH H 2 1 3 H OH 4 H H CH O 4 H OH HO 3 2 OH OH 5 CH2OH need C(3)-C(4) bond rotation to put OH in proper orientation to close 5-membered ring D-Ribose 5 5 HOCH2 OH H CH OH 1 2 1 4 H H CH O 4 H H CH O H 3 2 HO 3 2 OH OH OH OH D-Ribose 5 5 HOCH HOCH2 OH 2 1 OH H H 4 H H CH O O 4 1 H H 3 2 H 3 2 OH OH OH OH β-D-Ribofuranose CH2OH group becomes a substituent on ring Cyclic Forms of Carbohydrates: Pyranose Forms Carbohydrates Form Cyclic Hemiacetals 1 CH O 2 5 O OH 3 4 1 4 3 2 H 5 CH2OH cyclic hemiacetals that have 6-membered rings are called pyranose forms D-Ribose 1 CH O 5 H CH OH 2 2 H OH 1 4 H H CH O H 3 OH H 4 OH HO 3 2 OH OH 5 CH2OH pyranose ring formation involves OH group at C-5 D-Ribose H 5 5 H CH OH H O OH 2 1 H 4 H H CH O 4 H H 1 HO 3 2 H HO 3 2 OH OH OH OH β-D-Ribopyranose D-Ribose H H H 5 O OH H 5 O H H H 4 H H 1 4 H H 1 HO 3 2 H HO 3 2 OH OH OH OH OH β-D-Ribopyranose α-D-Ribopyranose D-Glucose 1 CH O 6 2 H OH 5 CH2OH H H HO 3 H 4 OH CH O OH H H 4 OH 1 5 3 2 H OH HO H OH 6 CH2OH pyranose ring formation involves OH group at C-5 D-Glucose 6 6 HOCH2 H OH 5 CH2OH H 5 H 4 H CH O 4 OH CH O OH H 1 OH H 1 HO 3 2 HO 3 2 H OH H OH need C(4)-C(5) bond rotation to put OH in proper orientation to close 6-membered ring D-Glucose 6 6 HOCH2 HOCH2 OH 5 H 5 H O OH H 4 H CH O 4 OH H 1 OH H 1 HO 3 2 H HO 3 2 H OH H OH β-D-Glucopyranose D-Glucose 6 6 HOCH2 HOCH2 H 5 O H H 5 O OH H H 4 OH H 1 4 OH H 1 HO 3 2 OH HO 3 2 H H OH H OH α-D-Glucopyranose β-D-Glucopyranose D-Glucose 6 HOCH2 H 5 O OH H 4 OH H 1 HO 3 2 H H OH β-D-Glucopyranose pyranose forms of carbohydrates adopt chair conformations D-Glucose 6 6 H HOCH2 HOCH2 H 5 4 OH 5 O H O HO H 4 OH H 1 HO 2 OH 3 1 HO 3 2 H H OH H H H OH β-D-Glucopyranose all substituents are equatorial in β-D-glucopyranose D-Glucose H H HOCH2 H HOCH2 H O O HO HO HO OH HO H 1 1 H OH H OH H H H OH β-D-Glucopyranose α-D-Glucopyranose OH group at anomeric carbon is axial in α-D-glucopyranose D-Ribose CH O H OH H OH H OH CH2OH Less than 1% of the open-chain form of D-ribose is present at equilibrium in aqueous solution.