Chemistry 2100 Chapter 20 Carbohydrates Molecular formula CH
Chemistry 2100 Chapter 20
Carbohydrates • Molecular formula (CH 2 O)n Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis. Monosaccharide: A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate. Aldose: A monosaccharide containing an aldehyde group. Ketose: A monosaccharide containing a ketone group.
Enantiomers
Monosacharides In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde. – D-monosaccharide: the -OH on its penultimate carbon is on the right in a Fischer projection. – L-monosaccharide: the -OH on its penultimate
Epimers
Hemiacetals and Hemiketals
Cyclization
1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 -D-glucose
Pyranoses and Furanoses
Haworth Projections D-Fructose (a 2 -ketohexose) also forms a five-membered cyclic hemiacetal.
-D(–)-fructofuranose -D(–)-fructopyranose (Honey)
Chair Conformations • For pyranoses, the six-membered ring is more accurately represented as a chair conformation
Chain-ring Equilibrium and Reducing Sugars
The Glycosidic Bond
Disaccharides
Sweetness Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol. Sweetness relative to sucrose:
starch
starch • amylose • amylopectin • dextrins
starch • amylose • amylopectin • dextrins
starch (1, 4) • amylose • amylopectin • dextrins
starch (1, 4) • amylose • amylopectin • dextrins
starch (1, 6) (1, 4) • amylose • amylopectin • dextrins
starch • amylose • amylopectin • dextrins
glycogen
cellulose β (1, 4)
Other Polymers Agar Chitin Heparin
(1 3) Blood Groups (1 4) Type A (1 2)
(1 3) Blood Groups (1 4) Type B (1 2)
(1 3) Blood Groups (1 4) Type O (1 2)
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