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Carbohydrates Classification of

Monosaccharide

is not cleaved to a simpler on hydrolysis , for example, is a monosaccharide Disaccharide is cleaved to two on hydrolysis these two monosaccharides may be the same or different

C12H22O11 + H2O C6H12O6 + C6H12O6

glucose (a monosaccharide) (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 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

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- 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 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 , , , and . 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 CH O Altruists Gladly Glucose Make Gum In H OH Gallon CH2OH Tanks 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: 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: 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. D-Ribose

76% of the D-ribose is a mixture of the α and β- pyranose forms, with the β-form predominating

H H H H H H O O HO HO H OH H H 1 H OH H OH OH H OH OH

β-D-Ribopyranose (56%) α-D-Ribopyranose (20%) D-Ribose

The α and β-furanose forms comprise 24% of the mixture.

HOCH2 HOCH2 OH H H O H H O H

H OH H H OH OH OH OH

β-D-Ribofuranose (18%) α-D-Ribofuranose (6%) Mutarotation

Mutarotation is a term given to the change in the observed optical rotation of a substance with time. Glucose, for example, can be obtained in either its α or β-pyranose form. The two forms have different physical properties such as melting point and optical rotation. When either form is dissolved in water, its initial rotation changes with time. Eventually both solutions have the same rotation. Mutarotation of 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

Initial: [α]D +18.7° Initial: [α]D +112.2°

Final: [α]D +52.5° Mutarotation of 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 Explanation: After being dissolved in water, the α and β forms slowly interconvert via the open- chain form. An equilibrium state is reached that contains 64% β and 36% α.