Aldehydes

and

Ketones

The Carbonyl Group

• In this and several following chapters,

we study the physical and chemical

properties of classes of compounds

containing the carbonyl group, C=O

– aldehydes and ketones

– Carbohydrates.

Structure– the functional group of an aldehyde is a

carbonyl group bonded to a H atom

– the functional group of a ketone is a carbonyl

group bonded to two carbon atoms

Propanone(Acetone )

Ethanal(Acetaldehyde)

Methanal(Formaldehyde)

O O O

CH3 CHHCH CH3 CCH3

Nomenclature• IUPAC names:

– the parent chain is the longest chain that

contains the carbonyl group

– for an aldehyde, change the suffix from -e to -al

– for an unsaturated aldehyde, show the carbon-

carbon double bond by changing the infix from -

an- to -en-; the location of the suffix determines

the numbering pattern

– for a cyclic molecule in which -CHO is bonded

to the ring, add the suffix -carbaldehyde

Nomenclature

CHO HO CHO

Cyclopentane-carbaldehyde

trans-4-Hydroxycyclo-

hexanecarbaldehyde

14

3-Methylbutanal 2-Propenal(Acrolein)

H

O

(2E)-3,7-Dimethyl-2,6-octadienal

(Geranial)

1

2

3

4

5

6

7

8

11

223

3

4H

O

H

O

2-Methyl-cyclohexanone

5-Methyl-3-hexanone

Benzophenone Acetophenone

OO

O O

Nomenclature

HCOOH

O

COOH

O

COOHHO

OHHS

COOH

NH2

-al oxo-

Ketone -one oxo-

Alcohol -ol hydroxy-

Amino -amine amino-

3-Oxopropanoic acid

3-Oxobutanoic acid

4-Hydroxybutanoic acid

3-Aminobutanoic acid

Example of When the FunctionalGroup Has a Lower Priority

Sulfhydryl -thiol mercapto- 2-Mercaptoethanol

Functional Group Suffix Prefix

Carboxyl -oic acid

Aldehyde

Nomenclature• Common names

– for an aldehyde, the common name is derived from

the common name of the corresponding carboxylic

acid

– for a ketone, name the two alkyl or aryl groups

bonded to the carbonyl carbon and add the word

ketone

Formaldehyde Formic acid Ace taldehyde Acetic acid

Ethyl isopropyl ketone Die thyl ke tone Dicyclohexyl ketone

OO

O

H H

O

H OH

O

H

O

OH

O

Physical Properties

• Oxygen is more electronegative than carbon (3.5 vs 2.5)

and, therefore, a C=O group is polar

– aldehydes and ketones are polar compounds and

interact in the pure state by dipole-dipole interactions

– they have higher boiling points and are more soluble

in water than nonpolar compounds of comparable

molecular weight

C O C O –

Polarity of acarbonyl group

-+C O

+

More importantcontributing

structure

::: : :

Reactions

• The most common reaction theme of a

carbonyl group is addition of a nucleophile

to form a tetrahedral carbonyl addition

compound

Tetrahedral carbonyl addition compound

+ C

R

R

O CNu

O -

RR

Nu -: :

::

:

:

Grignard Reagents

• Addition of carbon nucleophiles is one of the most

important types of nucleophilic additions to a C=O group

– a new carbon-carbon bond is formed in the process

• We study addition of carbon nucleophiles called

Grignard reagents

– Victor Grignard was awarded the Nobel Prize for

chemistry in 1912 for their discovery and application

to organic synthesis

– Grignard reagents have the general formula RMgX,

where R is an alkl or aryl group and X is a halogen

Grignard Reagents

• Grignard reagents are prepared by adding

an alkyl or aryl halide to a suspension of

Mg metal in diethyl ether

BrMg

MgBr+

1-Bromobutane Butylmagnesium bromide

ether

Br Mg MgBr+ether

Bromobenzene Phenylmagnesium bromide

Grignard Reagents

• Given the difference in electronegativity between carbon

and magnesium (2.5 - 1.3), the C-Mg bond is polar

covalent, with C- and Mg+

– in its reactions, a Grignard reagent behaves as a

carbanion

• Carbanion: an anion in which carbon has an unshared

pair of electrons and bears a negative charge

– a carbanion is a good nucleophile and adds to the

carbonyl group of aldehydes and ketones

Grignard Reagents• Reaction with protic acids

– Grignard reagents are very strong bases and react

with proton acids to form alkanes

– any compound containing an O-H, N-H, or S-H group

reacts with a Grignard reagent by proton transfer

CH3CH2-MgBr H-OH CH3CH2 -H Mg2+

OH-

Br-

Weaker base

Stronger base

Weaker acid

Stronger acid

pKa 51pKa 15.7

+++-

+ +

ArOH RSHRCOOHROHHOH RNH2

AminesAlcoholsWater Phenols ThiolsCarboxylicacids

Grignard Reagents

– reaction with formaldehyde gives a 1° alcohol

– reaction with any aldehyde other than formaldehyde

gives a 2° alcohol

Ph MgBr CH3 -C-H

O

Ph CHCH3

O

[MgBr]+

HCl

H2 OPh CHCH3

OH

Mg2+ether

A magnesium alkoxide

Acetaldehyde 1-Phenylethanol(a 2° alcohol)

++

CH3CH2 -MgBr H-C-H

O

CH3CH2-CH2

O [MgBr]+

HCl

H2OCH3 CH2-CH2

OH

Mg2+

Formaldehyde

+

A magnesiumalkoxide

+ether

1-Propanol(a 1° alcohol)

Grignard Reagents

– reaction with a ketone gives a 3° alcohol

– problem: show how to synthesize this 3° alcohol by

three different routes

Ph MgBr CH3 -C-CH3

O

Ph CCH3

CH3

O

[ MgBr]+

HCl

H2 OPh CCH3

OH

CH3

Mg2+ether

2-Phenyl-2-propanol(a 3° alcohol)

Acetone

++

A magnesiumalkoxide

CH3

C-CH2 CH3

OH

Addition of Alcohols

• Hemiacetal: a molecule containing an -OH group and an

-OR group bonded to the same carbon

– hemiacetals are minor components of an equilibrium

mixture except where a 5- or 6-membered ring can

form

CH3CCH3

O H

OCH2CH3H

+

CH3 C-OCH2 CH3

CH3

OH

A hemiacetal

+

4-Hydroxypentanal A cyclic hemiacetal(major form present at equilibrium)

OH

H

O

O

H

O

Hredraw to showthe OH close to

the CHO group O OH1

23

45

1

23

451

23

45

Addition of Alcohols

• Acetal: a molecule containing two -OR

groups bonded to the same carbon

CH3C-OCH2CH3

CH3

OH

CH3CH2OHH

+

CH3 C-OCH2CH3

CH3

OCH2CH3

H2 O

A diethyl acetal

++

A hemiacetal

OH

H

O

O OHCH3 OH

H+ O OCH3

H2 O

4-Hydroxypentanal

+

A cy clic acetal

Acetal Formation

1. Proton transfer from HA to the hemiacetal oxygen

2. Loss of H2O gives a cation

HO

H

R-C-OCH3H A

H

H

O

R-C-OCH3

H

A -

+

+

An oxonium ion

+

HO

R-C-OCH3

H

H

R-C

H

OCH3

H

R-C OCH3 H2O+

+

A resonance-stabilized cation

+

+

Acetal Formation3. reaction of the cation (an electrophile) with an alcohol

(a nucleophile)

4. proton transfer to A- gives the acetal and regenerates

the acid catalyst

CH3 -O

H

R-C OCH3

H

H

H

O

R-C-OCH3

CH3+

+

A protonated acetal

+

A

HO

R-C-OCH3

CH3

H

HA

H

O

R-C-OCH3

CH3

A protonated acetal An acetal

++

+

Imines

• Imine: a compound containing a C=N bond; also called a

Schiff base

– formed by the reaction of an aldehyde or ketone with

ammonia or a 1° amine

An imineAmmoniaCyclohexanone

++ NH3 H2OO NHH

+

CH3CH

O

H2N CH3 CH=N H2 O+ +

Ethanal Aniline An imine

H+

Imines1. addition of the amine to the carbonyl carbon followed

by proton transfer

2. two proton-transfer reactions and loss of H2O

C

O

H2N-R C

O

H

N-R

H

C

OH

N-R

H

-

+

A tetrahedral carbonyladdition intermediate

+

H

O H

H

C

OH

N-R

H

C

OHH

N-R

H

H

OH

C N-R H2 O H O

H

H

An imine

+

+

+++

Rhodopsin

– reaction of vitamin A aldehyde (retinal) with

an amino group on the protein opsin gives

rhodopsin

C=OH

H2N-Opsin+

C=H

N-Opsin

11

12

11-cis -Retinal

Rhodopsin(Visual purple)

Reductive Amination• Reductive amination: the formation of an imine followed

by its reduction to an amine

– reductive amination is a valuable method for the

conversion of ammonia to a 1° amine, and a 1° amine

to a 2° amine

+

Cyclohex-anone

Cyclohexyl-amine

(a 1° amine)

O-H2O

H+

H2N

Dicyclohexylamine(a 2° amine)

An imine(not isolated)

NH2 / Ni

N

H

Oxidation• Aldehydes are one of the most easily oxidized of all

functional groups

CHO

HO

MeO

Ag2OTHF, H2O

NaOH

HCl

H2 O

COOHMeO

HOAg

Vanillic acidVanillin

++

CHO H2CrO4 COOH

Hexanal Hexanoic acid

2 CHO O2 2 COOH

Benzoic acidBenzaldehyde

+

Reduction

– aldehydes can be reduced to 1° alcohols

– ketones can be reduced to 2° alcohols

R-CH

O

R-C-R'

O

R-CH-R'

OH

R-CH2 OH

A primaryalcohol

A secondaryalcohol

An aldehyde

reduction

A ketone

reduction

Catalytic Reduction

• Catalytic reductions are generally carried out from 25° to

100°C and 1 to 5 atm H2

– a carbon-carbon double bond may also be reduced

under these conditions

+25 oC, 2 atm

Pt

Cyclohe xanone Cyclohe xanol

O OH

H2

1-Butanol trans- 2-Bute nal

(Crotonalde hyde)

2 H2

NiH

O

OH

Carbohydrates

Monosaccharides

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

• Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate– monosaccharides have the general formula CnH2nOn

– the most common have from 3 to 9 carbons

– aldose: a monosaccharide containing an aldehyde group

– ketose: a monosaccharide containing a ketone group

Monosaccharides

– monosaccharides are classified by their

number of carbon atoms

hexose

heptose

octose

triose

te trose

pentose

FormulaName

C3 H6 O3

C4 H8 O4

C5 H10 O5

C6 H12 O6

C7 H14 O7

C8 H16 O8

Monosaccharides

– there are only two trioses

– often aldo- and keto- are omitted and these compounds are referred to simply as trioses

– although this designation does not tell the nature of the carbonyl group, it at least tells the number of carbons

CHO

CHOH

CH2OH

CH2OH

C=O

CH2OH

Dihydroxyacetone (a ketotriose)

Glyceraldehyde (an aldotriose)

Monosaccharides

• Glyceraldehyde contains a stereocenter

and exists as a pair of enantiomers

CHO

CH OH

CH2OH

CHO

C

CH2OH

HHO

(S)-Glycer-

aldehyde

(R)-Glycer-

aldehyde

Fischer Projection Formulas• Fischer projection: a two dimensional representation for

showing the configuration of a tetrahedral stereocenter

– horizontal lines represent bonds projecting forward

– vertical lines represent bonds projecting to the rear

– the first and last carbons in the chain are written in

full; others are indicated by the crossing of bonds

CHO

CH OH

CH2OH

CHO

H OH

CH2OH

(R)-Glyceraldehyde

convert to a Fischerprojection

(R)-Glyceraldehyde

D- and L-Monosaccharides

• In 1891, Emil Fischer made the arbitrary

assignments of D- and L- to the

enantiomers of glyceraldehyde

CHO

H OH

CH2OH

CHO

CH2OH

HHO

D D

L-GlyceraldehydeD-Glyceraldehyde

[]25

= +13.5° []25

= -13.5°

D- and L-Monosaccharides

• According to the conventions proposed by

Fischer

– D-monosaccharide: a monosaccharide that,

when written as a Fischer projection, has the -

OH on its penultimate carbon on the right

– L-monosaccharide: a monosaccharide that,

when written as a Fischer projection, has the -

OH on its penultimate carbon on the left

D- and L-Monosaccharides

• Following are

– the two most common D-aldotetroses and

– the two most common D-aldopentoses

D-Erythrose D-Threose D-Ribose 2-Deoxy-D-

ribose

CH2 OH

CHO

OH

OHH

H

CH2 OH

CHO

OH

HHO

H

CH2 OH

CHO

OH

OHH

H

CH2 OH

CHO

OH

HH

H

OHH OHH

D- and L-Monosaccharides

– and the three common D-aldohexoses

CHO

H

OHH

HO

OHH

D-GlucosamineD-Glucose D-Galactose

CH2 OH

OHH

CHO

H

OHH

HO

HHO

CH2 OH

OHH

CHO

H

NH2H

HO

OHH

CH2 OH

OHH

D- and L-Monosaccharides• Amino sugars

– N-acetyl-D-glucosamine is a component of many polysaccharides, including connective tissue such as cartilage; it is also a component of chitin, the hard shell-like exoskeleton of lobsters, crabs, and shrimp

CHO

OH

OH

H

NH2

H

H

HO

H

CH2 OH

CHO

OH

OH

H

H

H

H

HO

H2 N

CH2 OH

CHO

OH

OH

H

NHCCH3

H

H

HO

H

CH2 OH

OCHO

OH

H

H

NH2

H

HO

HO

H

CH2 OH

4

2

D -M an nosamin e

(C-2 stereoisomer

of D-g lucosamine)

D-Glucosamine D-G alactosamine

(C-4 stereo isomer

o f D-g lucosamine)

N -A cetyl -D-

g lucosamine

Cyclic Structure

• Monosaccharides have hydroxyl and

carbonyl groups in the same molecule and

exist almost entirely as five- and six-

membered cyclic hemiacetals

– anomeric carbon: the hemiacetal carbon of a

cyclic form of a monosaccharide

– anomers: monosaccharides that differ in

configuration only at their anomeric carbons

Haworth Projections– the anomers of D-glucopyranoseCHO

OH

H

OH

H

HO

H

H OH

CH2OH

H

H OH

HHO

HOH

OH

H

CH2OH

O

C

OH

HHO

HOH

H

CH2OH

OHO

H

OH

H OH

HHO

HH

OH

H

CH2OH

O

D-Glucose

-D-Glucopyranose (-D-Glucose)

()

()

-D-Glucopyranose

(-D-Glucose)

anomeric carbon

+

anomericcarbon

5

5

1

1

redraw to show the -OH on carbon-5 close to the

aldehyde on carbon-1

H

Haworth Projections

– 5- and 6-membered hemiacetals are represented as planar

pentagons or hexagons viewed through the edge

– most commonly written with the anomeric carbon on the right

and the hemiacetal oxygen to the back right

- means that -OH on the anomeric carbon is cis to the terminal -

CH2OH; - means it is trans

– a 6-membered hemiacetal is shown by the infix -pyran-

– a 5-membered hemiacetal is shown by the infix -furan-

OOPyranFuran

Cyclic Structures

• Aldopentoses also form cyclic hemiacetals

– the most prevalent forms of D-ribose and other

pentoses in the biological world are furanoses

– the prefix deoxy- means “without oxygen”

OH ()

H

HOH OH

H HO

HOCH2

H

OH ()

HOH H

H HO

HOCH2

-D-Ribofuranose

(-D-Ribose)

-2-Deoxy-D-ribofuranose

(-2-Deoxy-D-ribose)

Cyclic Structures

• D-Fructose, a 2-ketohexose, also forms a

cyclic hemiacetal

O

HO

HOCH2

H

H

HO

CH2OH

OHH

OH

HO

HOCH2

H

H

HO

H

H

HO

HOHOHOCH2

CH2OH

O

HCH2OH

OH

5

5

1

2

2

()

-D-Fructofuranose(-D-Fructose)

-D-Fructofuranose(-D-Fructose)

()

1

anomericcarbon

5

1

2

Conformational Formulas

– five-membered rings are close to planar so

that Haworth projections are adequate to

represent furanoses

O

OH()

H

HHO OH

H H

-D-Ribofuranose

(-D-Ribose)

O

H

OH()

HHO OH

H H

-D-Ribofuranose

(-D-Ribose)

HOCH2 HOCH2

Conformational Formulas

– the six-membered rings of pyranoses are more

accurately represented as chair conformations

O

H

HO

H

HO

H

H

OHHOH

OH

OH

H

HO

H

HO

H

HOHH

O

OH

O

H

HO

H

HO

H

OHOHH

H

OH

OH

H

HO

H

HO

H

OOHH

H

OH

-D-Glucopyranose

(-D-Glucose)[]

D = +18.7°

-D-Glucopyranose

(-D-Glucose)

[]D = +112°

rotate aboutC-1 to C-2 bond

Conformational Formulas

– compare the orientations of groups on

carbons 1-5 in the Haworth and chair

representations of -D-glucopyranose

– in each case, beginning at carbon 1, they are

up-down-up-down-up

OCH2OH

HOHO

OHOH()H

H OH

HHO

HOH()

OH

H

CH2OH

O

-D-Glucopyranose(chair conformation)

-D-Glucopyranose(Haworth projection)

1

23

4

5

6

1

23

4

5

6

Mutarotation

• Mutarotation: the change in specific

rotation that occurs when the or forms

of a carbohydrate are converted to an

equilibrium mixture of the two

+80.2

+80.2

+52.8

+150.7

-D-galactose

-D-galactose

[] after Mutarotation

(degre es)[]

Monosaccharide% Present at Equilibrium

28

72

64

36-D-glucose

-D-glucose

+112.0

+18.7

+52.7

+52.7

(degre es)

Mutarotation

• mutarotation of glucose

[] D25 + 18.7°

-D-Glucopyranose

-D-Glucopyranose

Open-chain form

( )

()

[] D25 + 112°

OHOH

HOHO

CH2 OH

OCH2 OH

O

HOHO

HOOH

OHO

C

CH2 OHHO

HO

HO H

Glycosides• Glycoside: a carbohydrate in which the -OH on its

anomeric carbon is replaced by -OR

H

H OH

HHO

HOH

OH

H

CH2OH

O

CH3 OH H+

-H2 O

O

CH2OH

H

OH

OCH3H

HOH

OHH

H

O

CH2OH

H

OH

HH

HOH

OHH

OCH3

(-D-Glucose)

-D-Glucopyranose

Methyl -D-glucopyranos ide

(Methyl -D-glucoside)

anomeric carbon

+

+

Methyl -D-glucopyranos ide

(Methyl -D-glucos ide)

glycos idicbond glycos idic

bond

Glycosides

• Glycosidic bond: the bond from the anomeric carbon of the glycoside to an -OR group

• To name a glycoside, name the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate; replace the ending -e by -ide

– methyl -D-glucopyranoside

– methyl -D-ribofuranoside

N-Glycosides– the anomeric carbon of a cyclic hemiacetal

also reacts with an N-H of an amine to form

an N-glycoside

– especially important in the biological world are

the N-glycosides of D-Ribose and 2-deoxy-D-

ribose with the following heterocyclic aromatic

amines

HN

N

H

O

O

Uracil

N

N

H

O

NH2

Cytosine

HN

N

H

O

O

Thymine

CH3N

N N

N

H

NH2

HN

N N

N

H

O

H2 N

Adenine Guanine

Pyrimidine bases Purine bases

N-Glycosides

– following is the -N-glycoside formed between

D-ribofuranose and cytosine

H

H

H

H

OHOCH2

HO OH

NH2

O

N

N

anomericcarbon

a -N -glycosid icbond

Reduction to Alditols

• The carbonyl group of a monosaccharide

can be reduced to an hydroxyl group by a

variety of reducing agents, including

NaBH4

OHOH

HOHO

CH2OHO

CHO

OHH

HHO

OHH

CH2 OH

OHH

NaBH4

CH2 OH

OHH

HHO

OHH

CH2 OH

OHH

D-Glucitol(D-Sorbitol)

D-Glucose

-D-Glucopyranose

Reduction to Alditols

– name alditols by replacing the -ose of the name of the

monosaccharide by -itol

– sorbitol is found in the plant world in many berries and

in cherries, plums, pears, apples, and seaweed; it is

about 60% as sweet as sugar

– other common alditols include

CH2 OH

CH2 OH

OHH

OHH

CH2 OH

CH2 OH

OHH

HHO

OHH

CH2 OH

HHO

HHO

OHH

CH2 OH

OHH

D-Mannitol XylitolErythritol

Oxidation to Aldonic Acids• The -CHO group can be oxidized to -COOH

– reducing sugar: any carbohydrate that reacts with an

oxidizing agent to form an aldonic acid

oxidizing

age nt

D-GluconateD-Glucose

C

OHH

HHO

OHH

CH2 OH

OHH

O H

C

OHH

HHO

OHH

CH2 OH

OHH

O O--D-Glucopyranose

(- D-Glucose)

OCH2 OH

HOHO

OHOH

basic

solution

Oxidation to Uronic Acids

• Enzyme-catalyzed oxidation of the 1°

alcohol at carbon-6 of a hexose gives a

uronic acidCHO

CH2 OH

OHH

HHO

OHH

OHH

CHO

COOH

OHH

HHO

OHH

OHH

HOHO

OHOH

COOHO

D-Glucose

enzyme-catalyzedoxidation

D-Glucuronic acid(a uronic acid)

Oxidation to Uronic Acids– the body uses glucuronic acid to detoxify foreign

alcohols and phenols

– these compounds are converted in the liver to

glycosides of glucuronic acid and then excreted in the

urine

– the intravenous anesthetic propofol is converted to

the following water-soluble glucuronide and excreted

O

OHOHO

OH

COO-

HO

Propofol A urine-soluble glucuronide

Glucose Assay

• The analytical procedure most often

performed in the clinical chemistry

laboratory is the determination of glucose

in blood, urine, or other biological fluid

– this need arises because of the high

incidence of diabetes in the population

Glucose Assay

• The glucose oxidase method is completely

specific for D-glucose

+

+

glucose

oxidase

D-Gluconic acid

Hydrogen

peroxide

- D-Glucopyranose

OHOH

HOHO

CH2 OHO

H2 O2

O2 + H2 O

CO2 H

CH2 OH

OHH

HHO

OHH

OHH

Glucose Assay– O2 is reduced to hydrogen peroxide, H2O2

– the concentration of H2O2 is proportional to the

concentration of glucose in the sample

– in one procedure, hydrogen peroxide is used to

oxidize o-toluidine to a colored product, whose

concentration is determined spectrophotometrically

NH2

CH3

H2 O2peroxidase

colored product+

2-Methylaniline(o-Toluidine)

Ascorbic Acid (Vitamin C)• L-Ascorbic acid (vitamin C) is synthesized

both biochemically and industrially from D-

glucose

CHO

CH2 OH

OHH

HHO

OHH

OHH

CH2 OH

OHH

HHO

O

OH

O

D-Glucose

both biochemialand industrial

syntheses

L-Ascorbic acid (Vitamin C)

Ascorbic Acid (Vitamin C)

– L-ascorbic acid is very easily oxidized to L-

dehydroascorbic acid

– both compounds are physiologically active

and are found in most body fluids

CH2OH

OHH

HHO

O

OH

O

CH2OH

OHH

HO

O

O

O

L-Ascorbic acid

(Vitamin C)L-Dehydroascorbic acid

oxidation

reduction

Sucrose

• Table sugar, obtained from the juice of

sugar cane and sugar beet

O

HO

OH

OH

CH2 OH

O

HO

HOO

CH2 OH

HOCH2

OHO

HO

O

OH

CH2 OH

HO

HOO

CH2 OH

HOCH2

1

1

2

1

2

1

-1,2-glycos idicbond

Sucrose

a unit of -D-

glucopyranose

a unit of -D-fructofuranose

Lactose

• The principle sugar present in milk

– about 5 - 8% in human milk, 4 - 5% in cow’s

milk

O

HO

HOOH

O

CH2 OH

O

HOOH

OH

CH2 OH

OHO O

OH

OH

CH2 OH

O OH

OH

OH

CH2 OH

1

1

4 4

-1,4-glycosidic bond

-1,4-glycosidic bond

Maltose

• From malt, the juice of sprouted barley

and other cereal grains

OHO

HOOH

OOHO OH()

OH

CH2 OH

CH2 OH

O

OH

O

OHHO

OOH()

HO

OH

CH2 OH

HOCH2 1

4

-1,4-glycosidic bond

1 4

Blood Group Substances

• Membranes of animal plasma cells have large numbers of relatively small carbohydrates– these membrane-bound carbohydrates are part of the

mechanism by which cell types recognize each other; they act as antigenic determinants

– among the first discovered of these antigenic determinants are the blood group substances

• In the ABO system, individuals are classified according to four blood types: A, B, AB, and O– at the cellular level, the biochemical basis for this

classification is a group of relatively small membrane-bound carbohydrates

Blood Group Substances

– one of these membrane-bound

monosaccharides is L-fucose

HHO

OHH

CH3

CHO

OHH

HHO

An L-monosaccharide;this -OH is on the left in

the Fischer projection

L-Fucose

Carbon 6 is -CH3 ratherrather than -CH

2OH

Blood Group Substances

• A, B, AB, and O blood types

N -Acetyl-D-

galactosamineD-Galactose N-Acetyl-D-

glucosamine

D-GalactoseN-Acetyl-D-

glucosamine

Redblood

cell

Type A

Type B

D-GalactoseType O N-Acetyl-D-

glucosamine

Redblood

cell

Redblood

cell

D-galactose

(-1,4)

(-1,4)

(-1,3)

(-1,3)

(-1,3)

L-Fucose

(-1,2)

L-Fucose

(-1,2)

L-Fucose

(-1,2)

Starch

• Starch is used for energy storage in plants

– it can be separated into two fractions; amylose and amylopectin

– amylose is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds

– amylopectin is a highly branched polymer of D-glucose; chains consist of 24-30 units of D-glucose joined by -1,4-glycosidic bonds and branches created by -1,6-glycosidic bonds

Starch

Glycogen

• The reserve carbohydrate for animals

– a nonlinear polymer of D-glucose units joined

by -1,4- and -1,6-glycosidic bonds

– the total amount of glycogen in the body of a

well-nourished adult is about 350 g (about 3/4

of a pound) divided almost equally between

liver and muscle

Cellulose

• Cellulose is a linear polymer of D-glucose

units joined by -1,4-glycosidic bonds

– it has an average molecular weight of

400,000, corresponding to approximately

2800 D-glucose units per molecule

– both rayon and acetate rayon are made from

chemically modified cellulose