b.sc. iii chemistry - govt.college for girls sector 11...
TRANSCRIPT
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