Chemistry 2100 Lecture 9. Carbohydrates Molecular formula (CH 2 O) n Carbohydrate: Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone, or a substance.

Chemistry 2100

Lecture 9

Carbohydrates

• Molecular formula (CH2O)n

Carbohydrate:Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis.

Monosaccharide:Monosaccharide: A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.

Aldose:Aldose: A monosaccharide containing an aldehyde group.Ketose: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:D-monosaccharide: the -OH on its penultimate carbon is on the right in a Fischer projection.

– L-monosaccharide:L-monosaccharide: the -OH on its penultimate carbon is on the left in a Fischer projection.

L-GlyceraldehydeD-Glyceraldehyde

CHOCHO

H OH

CH2OH CH2OH

HHO

[]25 = +13.5°D

[]25 = -13.5°D

Epimers

Hemiacetals and Hemiketals

Cyclization

C

CH2OH

OHH

HO H

H OH

H

O HH

O

C

CH2OH

OHH

HO H

H OH

H O

H

H

O1

2

3

5

6

4

-D-glucose -D-glucoseD-glucose

1

2

3

5

6

4

1

2

3

5

6

4

C

CH2OH

OHH

HO H

H OH

H

OH H

O

Pyranoses and

Furanoses

Haworth ProjectionsD-Fructose (a 2-ketohexose) also forms a five-membered cyclic hemiacetal.

HO

HOCH2 OH

HHO

CH2OH

OHH

H

C=O

CH2OH

HOH

CH2OH

OHH

HO HOH

HOHOCH2

HO HCH2OH

OH

D-Fructose

1

2

5

5

5

1

2

2

()

-D-Fructofuranose(-D-Fructose)

-D-Fructofuranose(-D-Fructose)

()

1

O

CH2OH

OHOH

HOCH2

HO

O

HOHO

OHOH

CH2OH

-D(–)-fructofuranose -D(–)-fructopyranose

(Honey)

Chair Conformations• For pyranoses, the six-membered ring

is more accurately represented as a chair conformationchair conformation.

OCH2OH

HOHO

OHOH()

CHOH

HO

CH2OHOHHO

OHO

OH()HO

HO

CH2OHO

(-D-Glucose)

(-D-Glucose)

-D-Glucopyranose

-D-Glucopyranose

D-Glucose

anomericcarbon

Chain-ring Equilibrium and Reducing Sugars

The Glycosidic

Bond

Disaccharides

SweetnessMonosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol.

Sweetness relative to sucrose:Carbohydrate

fructose

glucose

galactose

sucrose (table sugar)

lactose (milk sugar)

honey

SweetnessRelative to Sucrose

1.741.000.970.74

0.320.16

Artificial Sweetener

SweetnessRelative to Sucrose

maltose 0.33

saccharin 450acesulfame-K 200aspartame 180sucralose 600

starch

• amylose

• amylopectin

• dextrins

starch

• amylose

• amylopectin

• dextrins

starch

• amylose

• amylopectin

• dextrins

(1,4)

starch

starch

• amylose

• amylopectin

• dextrins

(14)

starch

• amylose

• amylopectin

• dextrins

(16) (14)

starch

• amylose

• amylopectin

• dextrins

glycogen

β(1,4)

cellulose

Other Polymers

Chitin

Agar

Heparin

Lipids

Fatty Acids

COOH

oleic acid (mp 4°C)

stearic acid (mp 70°C)

COOH

Triacylglycerols

Saponification• Saponification: the base-promoted

hydrolysis of fats and oils in aqueous NaOH and produces glycerol and a mixture of fatty acid salts called soaps.

O

CH2OCR

CH2OCR

RCOCH

O

O

CH2OH

CH2OH

HOCH RCO-Na+

O

A triglyceride 1,2,3-Propanetriol(Glycerol, glycerin)

+

Sodium soaps

3saponification

anionic detergents

(-HOH)

sodium lauryl sulfate

S

O

O

O NaCH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2O

NaOHH2SO 4CH3(CH2)10CH2O S

O

O

OHCH3(CH2)10CH2OH

lauryl alcohol

Synthetic Detergents (syndets)

Hydrogenation

Hardening: The reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H2/transition metal catalyst, which converts a liquid triglyceride to a semisolid.

"partially hydrogenated vegetable oil"

+

COOH

COOH

COOH

H2 catalyst

• •

Complex Lipids

Figure 21.1 Schematic diagram of simple and complex lipids.

Membranes: Glycerophoshpolipids

Fluid Mosaic Model

Figure 21.2 The fluid mosaic model of membranes.

O

O

O

O

Other Lipids: Waxes

Sterols

Steroids RU-486

O

HO

C C CH3

Me2N

cholesterol

HO

progesterone

O

O testosterone

O

OH

estradiol

HO

OH

Low-Density Lipoprotein