B.sc. III Chemistry Paper b

Submited by :-

Dr. Sangeeta Mehtani

Associate Professor

Deptt. Of Chemistry

PGGCG, sec11

Chd

CARBOHYDRATES

Carbohydrates – polyhydroxyaldehydes or polyhydroxy-

ketones of formula (CH2O)n, or compounds that can be

hydrolyzed to them. (aka sugars or saccharides)

Carbohydrates are classified into following-:

Monosaccharides – carbohydrates that cannot be hydrolyzed

to simpler carbohydrates; eg. Glucose or fructose.

Disaccharides – carbohydrates that can be hydrolyzed into

two monosaccharide units; eg. Sucrose, which is hydrolyzed

into glucose and fructose.

Oligosaccharides – carbohydrates that can be hydrolyzed

into a few monosaccharide units.

Polysaccharides – carbohydrates that are are polymeric

sugars; eg Starch or cellulose.

Monosaccharides

C

C OHH

C HHO

C OHH

C OHH

CH2OH

D-glucose

OH

C HHO

C OHH

C OHH

CH2OH

CH2OH

C O

D-fructose

Aldoses (e.g., glucose) have

an aldehyde group at one end.

Ketoses (e.g., fructose) have a

keto group, usually at C2.

Aldose – polyhydroxyaldehyde, eg glucose

Ketose – polyhydroxyketone, eg fructose

Triose, tetrose, pentose, hexose, etc. – carbohydrates that

contain three, four, five, six, etc. carbons per molecule

(usually five or six); eg. Aldohexose, ketopentose, etc.

D vs L Designation

D & L designations

are based on the

configuration about

the single asymmetric

C in glyceraldehyde.

The lower

representations are

Fischer Projections.

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

L-glyceraldehydeD-glyceraldehyde

L-glyceraldehydeD-glyceraldehyde

Sugar Nomenclature For sugars with more

than one chiral center,

D or L refers to the

asymmetric C farthest

from the aldehyde or

keto group.

Most naturally occurring

sugars are D isomers.

O H O H

C C

H – C – OH HO – C – H

HO – C – H H – C – OH

H – C – OH HO – C – H

H – C – OH HO – C – H

CH2OH CH2OH

D-glucose L-glucose

CHO

OHH

HHO

OHH

OHH

CH2OH

(+)-glucose

Exists only in solution. There are two

solids:

α-glucose m 146o [α] = +112.2

β-glucose m 150o [α] = +17.5

In water each mutarotates to an

equilibrium with [α] = +52.7

(63.6% β / 36.4% α)

(+)-glucose? An aldohexose

Emil Fischer (1902)

Four chiral centers, 24 = 16 stereoisomers

Reducing sugar – a carbohydrate that is oxidized by Tollen’s,

Fehling’s or Benedict’s solution.

Tollen’s: Ag+ Ag (silver mirror)

Fehling’s or Benedict’s: Cu3+ (blue) Cu2+ (red ppt)

These are reactions of aldehydes and alpha-hydroxyketones.

All monosaccharides (both aldoses and ketoses) and most*

disaccharides are reducing sugars.

*Sucrose (table sugar), a disaccharide, is not a reducing sugar.

Chemical Properties of D+

Glucose

Osazone Formation

1.

2.

Ruff degradation – a series of reactions that removes the

reducing carbon ( C=O ) from a sugar and decreases the

number of chiral centers by one; used to relate configuration.

CHO

H OH

CH2OH

H OH

CO2H

H OH

CH2OH

H OH

Br2

H2O

CO2

H OH

CH2OH

H OH

Ca2+

H2O2

Fe3+

CHO

CH2OH

H OH

D-(+)-glyceraldehyde

Kiliani-Fischer synthesis.

A series of reactions that extends the carbon chain in a

carbohydrate by one carbon and one chiral center.

CHO

H OH

CH2OH

HCN

C

H OH

CH2OH

H OH

C

HO H

CH2OH

H OH+

N N

H+,H2O

COOH

H OH

CH2OH

H OH

COOH

HO H

CH2OH

H OH

diastereomersseparable

C

H OH

H2C

H OH

O

O

lactone

Na(Hg)

CHO

H OH

CH2OH

H OH

-H2O

Epimers – stereoisomers that differ only in configuration about

one chiral center.

CHO

OHH

HHO

OHH

OHH

CH2OH

D-glucose

CHO

HHO

HHO

OHH

OHH

CH2OH

D-mannose

epimers

Configuration of Glucose

CHO

H OH

CH2OH

H OH

aldotetrosesCH2CHCHCH O

OH OHOH

* *

CHO

HO H

CH2OH

HO H

CHO

H OH

CH2OH

HO H

CHO

HO H

CH2OH

H OH

D-erythrose L-erythrose

L-threose D-threose

RING STRUCTURE OF GLUCOSE

CHO

OHH

HHO

OHH

OHH

CH2OH

O

H

HO

H

HO

H

OHOHH

H

OH

O

H

HO

H

HO

H

HOHH

OH

OH

alpha-(+)-glucose beta-(+)-glucose

OH

OH

OH

H

H

OHH

OH

CH2OHOH

OH

H

OH

H

OHH

OH

CH2OH

RC

H

O

+ R'OH R C H

OH

OR'

R C H

OR'

OR'

hemiacetalgeminalether/alcoholreducing!

acetalgeminaldiethernon-reducing!

GLYCOSIDES:

Addition of alcohols to aldehydes/ketones:

CHO

OHH

HHO

OHH

OHH

CH2OH

O

H

HO

H

HO

H

OHOHH

H

OH

O

H

HO

H

HO

H

HOHH

OH

OH

nucleophilic addition of -OH on carbon 5 to the aldehyde functional group

CHO

OHH

HHO

OHH

OHH

CH2OH

CH

OHH

HHO

OHH

HHOH2C

OH

O

H

HO

H

HO

H

OHOHH

H

OH

O

O

H

HO

H

HO

H

HOHH

OH

OH

rotate C-5 OH to rear

O

H

HO

H

HO

H

HOHH

OH

OH

O

H

HO

H

HO

H

OHOHH

H

OH

hemiacetal

4H-Pyran

OD-glucopyranoses

alpha beta

Thank you