Chemistry 2100 Lecture 9 Carbohydrates Molecular formula CH

Chemistry 2100 Lecture 9

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 (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

Lipids

Fatty Acids

oleic acid (mp 4°C) stearic acid (mp 70°C)

Triacylglycerol s

Saponification • Saponification: the base-promoted hydrolysis of fats and oils in aqueous Na. OH and produces glycerol and a mixture of fatty acid salts called soaps.

Synthetic Detergents (syndets) anionic detergents

Hydrogenation Hardening: The reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H 2/transition metal catalyst, which converts a liquid triglyceride to a semisolid.