Stereochemistry of carbohydrates :

D&L-Sugars: The series of aldoses or ketoses in which the configuration of the penultimate
C-atom (C-next to CH,-OH group) is described as D-sugars if -OHis towards RHS &L-sugars if it
is towards LHS.
CHO
Smallest carbohydrate * Aldotriose
CH-OH
Glyceraldehyde
CH,OH

CHO CHO

H- -OH HO
H,OH CH,OH
D-Glyceraldehyde (+) L-Glyceraldchyde (-)

Classification of Aldotetros :i) Erythrose

(ii) Threoese

C-4 CHO CHO CHO CHO

H-OH HO -H
H
H,OH
-OH
H,OH
HO +
H,OH
H HO
CH,OH
-H

D-Erythrose D-Threose L-Erythrose L-Threose

D-Aldopentose :
C-5 CHO CHO

(CHOH), HOH
(HOH),
H-oH CH,OH
CH,OH
D-Aldopentose L-Aldopentose

No. of C*=3 (in Aldopentose)

No. of optical isomers 2 =8
No. of D Sugars 4

No. of L Sugars 4

CHO CHO CHO CHO

H -OH H OH HO -H HO -H
H OH HO H H -OH HO -H
H -OH H OH H -OH H OH
CH,OH CH,OH CH,OH CH,OH
() (W (II) (1V)

All Isomeric D-sugars are diastereomers.

 D-Aldohexose : CHO CHO
No. of C* =4 H -OH HO H
HO -H H OH
No. of stereoisomers = 2+ =16
No. of D-sugars = 8
H-oH HO H
H -OH HO -H
No. of L-sugars = 8 CH,OH H,OH
D-Glucose L-Glucose
The D-family aldoses
CHO
H- -0H

CH,OH
-D-glyceraldehyde -
CHO CHO

H-C-OH HO--H
H-C-OH H-C-OH
CH,OH CH,OH
-D-erythrose -D-threose
CHO CHO CHO CHO

H--OH HO-c-H H-C-OH HO-C-H

H--OH H-C-0H HO-C-H HO-C-H
H--OH H-C-OH H-C-OH H--OH

CH,OH CH,OH CH,0H CH,OH

D-ribose D-arabinose D-xylose D-lyxose

CHO CHO CHO CHO CHO CHO

CHO CHO
H-C-OH HO-C-H H-C-OH HO -C-H H-C-OH HO-C-H
H- -0H HO--H
H-C-0H H-C-OH HO -C-H H-C-OH H-C-OH HO --H
HO -C-H
HO--H
H-C-OH H-C-OH H-C-OH H-C-OH HO-C-H HO-C-H HO - -H HO-H
H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-
C-OH H-C-OH
CH,OH CH,OH CH,0H CH,OH CH,OH CH,OH H,OH H,0H
D(+)allose D(+)altrose D(+)glucose D(+)mannose D(-)gulose D(-)idose D(+) galactose D(+)talose
Epimers: A pair of diastereomers that differ only in the configuration about of a single carbon atom
are said to be epimers. D(+)-glucose is epimeric with D(+)- mannose and D(+)-galactose as shown below.
Epimers Epimers
CHO CHO CHO

H-C-0H H-- OH HO C-H

HÌ CH HO C- I H HO-C
(HO -C-H H-C-OH H-C-OH

H-C-OH H-C-OH H-C-OH

CH,OH CH,OH H,0H
D(+) galactose D(+) glucose D(+) mannose
|C, is epimeric carbon | |C, is epimeric carbon
Another example with C, epimeric carbon is
ÇHO CHO
H -OH HO -H
H -OH H OH
H -OH
& H -OH
CH,OH CH,OH
D-ribose D-arabinose
Anomers: Anomers are the stereoisomers which differs at a single chiral centre out of many & are
ring chain tautomer of the same open chain compound.
The two sugars that differs in configuration only on the carbon that was the carbonyl carbon in the
open chain form is called as anomers a glucose and Bglucose are known as anomers their equilibrium
mixture contains 36 % a-D-glucose , 63.8 % B-D-glucose and 0.2 % open chain form.
C, Carbon is known as anomeric carbon.
Haworth suggested to write oa glucose and Bglucose in pyran structure
CHO
H -HO OH HO -H
-H H OH
H -HO HO
HO -H H -OH HO -H
H -OH H -OH
H -OH H
H
CH,OH CH,OH CH,0H
a-D-glucose D-gucose (open structure) B-D-glucose
(sp rotation 112°) (sp rotation 19°)
ÇH,OH ÇH,OH
HH OH
HO OH HO OH
gH H
OH ÖH
Haworth formula Haworth formula

a-D-glucopyranose B-D-glucopyranose
AnomerS are epimers but epimers may not be anomers.
 Anomeric effect:
B-D-glucose is more stable then a-D glucose because there is more room for a substituent in the
equatorial position. However when glucose reacts with an alcohol to form a glucoside, the major
product is the a-glucoside. The preference for the axial position by certain substituents bonded to
the anomeric carbon is called anomeric effect.

CH,
The anomeric substituent
is in the fß-position
H,C
The anomenc substituent
is in the a-position

What is responsible for the anomeric effect ? One clue is that all the substituents that prefer the axial
position have lone pair electrons on the atom bonded to the ring. The lone pair electrons of the
anomeric substituent have repulsive interaction with the lone pair electron of the ring oxygen if the
anomeric substituent is the B-position , but not if it the a-position.
Apparently attractive interaction of the hydrogen of the anomeric OH group of D-glucose with the
lone pair electron of the ring oxygen decreases the importance of the anomeric effect making
B-D glucose more stable than a-D glucose. However, when the hydrogen is replaced by an alkyl
group, the anomeric effect decreases the stability of the B-position so, a-glycosides are more stable
than B-glycosides.
Cyclic structures of monosaccharides
Many five membered and six membered monosaccharides occur in cyclic form. Cyclic structures of
monosaccharides are established by many experiments. The cyclic structure is due to intramolecular
hemiacetal formation between aldo / keto group and OH of any one carbon. The ring formed are
generally six membered (pyranose) or five membered (furanose). Each cyclization results in creation
of a new asymmetric centre apart from the existing ones. The isomers resulting from cyclizations are
called anomers. example, when D-glucose (open structure) cyclise, it gives a-D-glucose and
B-D-glucose.
Haworth projection:
Many of monosaccharides form cyclic structures. The actual structure is almost planer and be
represented by Haworth projection, which is a way of depicting three -dimensional cyclic structure.
Rule -1 ; In a Haworth projection draw a fisher projection in which ring oxygen is in a down
position.
Rule -2 - Imagine that carbon chain of fisher projection is folded around a barrel or drum,
which provide a ring lies in a plane I to the page.
Rule -3 : Now plane of ring is turned 90° so that anomeric carbon is on the right and the ring
Oxygen is in the rear. Obtained projection is a Haworth projection.
Example : (D-glucose)
OH H OH
H
OH HH OH HO

CHO OH
CHO CH,OH
CH,OH H OHI
CH,OH -CHO
H OH H OH
OH
OH H OH H
Projection:
H
CH,OH CH,OH
HO HO
H OH H

H H lllu
CHO
OH
OH OH
H
OH H OH H

Hawarth projection
’ Chair conformation of D-glucose
ÇH,OH
H H
H,OH OH
HO H
HO
HC
HÓ
OH
OH
Chair forms of (conformation) a and BD-Glucose :
CH,OH
CH,OH 0 OH
OH OH
Hâ anomeric
OH carbon
HO OH
OH
B-D-Glucose (most stable glucose form) all groups are equatorial.
CH,OH
CH,OH0,
H anomenic
OH
HO carbon
HO OH
OH
a-D-Glucose -OH group at anomeric carbon is axial.
Mutarotation
CH,OH 0 H,0 CH,OHo
-OH
Hâ" acid HO"
OH or base OH
HO HO
-anomer B-anomer
Specific rotation of aglucose + 112° Specific rotation of Bglucose + 19°
Equilibrium mixture [a],= 52.5 degree mL g- dm-l
Fresh a-glucose ’ 52.5 + Fresh B-glucose
112° 36 % a glucose 19°
63.8 % Bglucose
When pure a-D glucose is dissolved in water its specific rotation is found to be +112° with time,
however the specific rotation of the solution decreases ultimately reaches stable value of +52.5°.
When ß D-glucose is dissolved in water, it has a specific rotation of 19°. The specific rotation of this
solution increases with time also to + 52.5 °.
This change of optical rotation with time is called mutarotation. It is caused by the conversion of
a and ß glucopyranose anomers into an equilibrium mixture of both. Mutarotation is catalyzed by
both acid and base, but also occurs is even in pure water. Mutarotation is characteristic of the cyclic
hemiacetal form of glucose.
Mutarotation occurs first by opening of the pyranose ring to the free aldehyde form.

CH,0H CH,OHLOH
H,0» or QH
Hã Hâ
HO
HO
OH HO OH OH
CL-anomer lrotation

CH,OHo H,o*, OH CH,OH OH

OH closing of hemiaceta OH
Hâ |Hâ
HO OH
HO HO
B-anomer

Structure of fructose
fH-OH HO-¢-CH,OH
HOH,C-(-OH HO-C-H
HO-C-H O

H-¢-OH HO ¢H H-C-OH
H- OH H-¢-OH
H--OH
Hc OH H-C
H-
CH,-OH
a fructose B fructose (more stable)

Ring structure of fructoseC, Pyranose structures 6 membered ring, C,-C, linkage

H

-ÇH;OH
OH
OH OH
OH OH VCH,OH
Chair conformations
ÒH
 OH
ÇH;OH
OH CH,OH
|HO HO LOH
LOH
OH OH

a-D-fructopyranose B-D-fructopyranose
Furanose structure (5 membered ring)

HOH,Ç OH HOH,Ç CH,OH

HO
CH,OH
OH
BD-fructofuranose C-D-fructofuranose

Mutarotation: Fructose undergo complex mutarotation. The structure of the cyclic hemiacetal
form of d-fructosecan be derived from it's carbonyl (Ketone) form using the methods described as
follows.

ÇH;OH
HO -H ÇH,OH
H OH C=0
H -OH HO H
H
CH,OH OH
H OHe This orygen is
invoved in
Ihis structure is CH,OH furanose formation
ivolved in pyranose
formation

It happens that the crystalline form of D-fructose is B-D-Fructopyranose. When crystals of this form
are dissolved in water, it equilibrates to both pyranose & furanose forms.
OH anomeric
carbon CH,OHanomeric
carbon
~CH,OH OH
H ZOH |HO OH
OH OH
B-D-fructopyranose a-D-fructopyranose

HOCH,OH HOH;Ç OH HOH,C OH CH,OH

-anomeric
carbon
HOH,Ç lanomeric
carbon
HO -H HÌ/ HO- -H
Y/CH,OH HO
OH
H -OH Î H-OH )
ÒH
H
B-D-fructofuranose H OH
H,OH H,OH a-D-fructofuranose
All monosaccharides are reducing sugars and they show mutarotation.
Starch, cellulose are Polymers of Glucose
Lactose and sucrose are disaccharides
Sucrose is a non reducing sugar, gives negative test for Benedict and tollen's reagent, they do not
form osazone and do not show mutarotation.
Acetals of carbohydrates are called as GLYCOSIDE
Formation of Glycosides
Glucose reacts with methyl alcohol in presence of dry HCl to form a and B-methyl glycoside of
glucose. The reaction takes place only on OH of hemi-acetylic carbon. Other hydroxyl groups are
unreactive.
H OCH, CH,O H

(CHOH), (CHOH), o
CH CH
CH,OH CH,OH
-Methyl glucose B-Methylglucose
To methylate all the OH groups, methylating agent used is dimethyl sulphate.
CH,OH
CH,0H
HCI HO H
+ CH,OH HO OH
HO wwwOH
HO OH OCH,

D-glucose methyl a-D-glucopyranoside

ÇH,OH
HO OCH,
HO OH
H

methyl p-D-glucopyranoside
+ H,0

Such compounds are called glucoside (cyclic acetals). They are special type of acetals in which one
of the oxygen of the acetal linkage is the ring oxygen of the pyranose or furanose.
Ring structure of glucose:
() Glucose does not give pink colour with schief reagent. HC-OH
(ü) Does not form adduct with NaHSO,, NH, HO-C-H
(iil Glucose exist in two isomeric form H-C-OH

(iv) It show mutarotation

CH,OH
 Since there is no free aldehyde group, so it does not react with weak reagent
(NH,, NaHSO,) but strong reagent (HCN, NH,OH, CcH,NH - NH) break up ring
OH
H-OH
H¢OH H-c-oH
H-C-OH HO-C-H CHO
Hydrolysis
HC-OH -H;0’ HOH
H--OH H -OH H,OH
H-OH
- OH
H
REACTIONS OF GLUCOSE
COOH
(HOH), Br,/ H,0 Red P/HI n Hexane
H,OH or Alkaline
Gluconic acid solution ofl, CH,COCI
Pentaacetate
ÇoONH
Tollen's
(5-OH group)
CHOH)4 -CoH;0%
NH,-OH (leq) Oxime
Salts of CH,OH
gluconic acids HCN
ÇOONa Fehling's
Glucose cyanohydrin
(HOH), SHIO,
HCHO + 5HCOOH
H,OH
ÇOOH Schief's reagent, NaHSO, No reaction
HNO,
(HOH), NH,
COOH
(Saccharic acid)

These reactions indicate that glucose has 6-C straight chain with one -CHO group & 5-OH group.
General reactions of monosaccharies
CHO CHOH
Ç-O
(CHOH),
CH,OH (CHOHW),
CH,OH
Glucose Fructose
Base-catalyzed isomerisation of aldoses and Ketoses:
Although glucose in solution exists mostly in its cyclic hemiacetal forms it is also in equilibrium
with a small amount of it's acyclic aldehyde form.

CHO CHO CHO CH,OH

H -OH
0.02M H -OH HO -H
HO H Ca(OH)2 HO HO -H
H -OH H -OH H -OH
+
HO-C-H + Traces of other compound
H -OH H -OH H -OH -OH

CH,OH CH,OH
recovered
CH,OH
D-mannose
H
CH,OH
oH
Dglucose D-Fructose

Method of ascending the sugar series: An aldose may be converted into it's next higher
aldose eg. an aldopentose into an aldohexose.

By Kiliani Fischer upgradation:

CHO ÇHO
ÇHOH CHOH CHOH
HCN (ÖH>Pd
CHOH ag. çHOH (ii) BaSO4
H0 CHOH
ÇHOH ÇHOH ÇHOH
H,OH CHOH
CHOH
CH,OH
CH,OH
Theoretically two lactones are possible, since two cyanohydrin may be formed when hydrogen
cyanide adds on to the aldopentose (a new assymetrical carbon is produced)

CN
HCN’ H -OH + HO H

Wolfrom reaction : Wolfrom have stepped up an aldose to a ketose with one more carbon
atom by a modified Amdt-Eistere reaction.

CHO COOH COCI CHN, CH,OH

CHOH),
Br
(HOH), () Ac,0 ’ (ÇHOAc); CH)N,, C0 (i)AcOH
(ü)Ba(OH):
CH,OH H,0
H,OH
(ü)SOCI)
CH,OAe CHOAC); cHOH,
CH,OAE H,OH
 Method of descending the sugar series:
Wohl's method:

CH=N-OH CN
CHO

CHOH CHOH CHO

NH,OH (CH,CO)o aq AgOH
(ÇHOH), +AgCN
(CHOH)} CHOH), A.excess
CH,OH
HÌH CH,OH
H-OfCH
Ruff's method:

CHO COOH
CHO
CHOH HOH
Ca salt
(çHOH), B,/H;0 ,(ÇHOH); H,0,/Fe+ + CO,
H;OH CH,OH Fenton's
reagent
CH,OH

Conversion of an aldose into a ketose :

CHO CH=N-NH-CGHs CHO

HOH -N-NH-CHs C-0 CH,OH
R
3C6HsNHNH)
R
HCI, Î Zn/CHCOOH C-0
R
Glucose Osazone Osone R
Fructosc

An aldehyde group is reduced more readily than a ketonic group.

Conversion of a Ketose into an aldose :

COOH CO CHO
CH,OH CH,OH
CHOH Na/Hg , CHOH
C=0 H,/Ni *ÇHOH ’ CHOH A

R R
HNO;
R
ÇHOH HCI
R
INew assymetric CH
Cso, wo products
ÇHOH
CH,OH
VLactone
 TEST OF CARBOHYDRATES
1. Molish Test 2. Barfoed Test 3. Salivanoff's Test. 4. Bial's Test
5. Osazone Test 6.Benedict Test 7. Fehling Test 8. Tollen's Test
9. lodine Test
1. Molish Test
Molish test is the general test for the identification of all carbohydrates (Monosaccharides,
Disaccharides and Poly saccharides ) and Glycoprotein, Sulphuric acid is added to hydrolyzes the
all glycosidic linkage to yield monosaccharides, which on dehydration form furfural or its derivative
in presence of acid.which condened with a-naphthol to give a violet colored complex.

Oligosaccharide or poly saccharides + H,SO, H,0* (Hydrolysis) Monosaccharides

HO
HO H HO,
HO -3H,0
OH OH
5-(hydroxymethyl) furfural
D-glucose (monosaccharide)

OH OH
H.O» HO, [0j. H,0* HO
HO, 2
-H,0 -H,-2e
a-naphthol
5-(hydroxymethyl) furfural
OH
purple colored dye
or

violet colored complex

2. Barfoed Test
This test is used to differentiate reducing monosaccharide from a disaccharide sugar
It is done in mild acidic medium.

RCHO + 2Cu²* + 2H,0 ’ RCOOH + Cu,0 ppt + 4H*

It is based on the reduction of copperl) acetate to copper() oxide (Cu,O), which forms a brick
red precipitate.
Reducing monosaccharides react with Barfoed's reagent much faster than disaccharides and produce
red precipitate of copper (I) oxide within three minutes.
Disaccharide sugars as they are weaker reducing agents, react at a slower rate, so they do not form
red precipitate even for ten minutes.
3. Selivanoffs Test

It is test of Ketose sugar (eg Fructose), it is used to differentiate Ketose sugar from aldose sugar.
This test relies on the principle that keto hexose are more rapidly dehydrated than aldoses to form
5-Hydroxy methyl furfural when heated in acidic medium, which on condensation with resorcinol,
a cherry red (or Brown red) colored complex is formed rapidly indicating a positive test.
 HO.
CH,OH CH,OH ÇH,0H CHO
[H"] [H*) 0.5 O,
HO
OH -3 H,0
OH

OH 3 H,0
2
oH CH,OH

Fructose Resorcinol Cherry red ppt

4. Bial's Test
Bial's test is positive for Pentoses
This test is used to differentiate Pentose and Hexose sugar
The test reagent dehydrates pentoses to form furfural. Furfural further reacts with Bial's reagent (a
solution of orcinol, HCl and ferric chloride). orcinol and the iron ion present in the test reagent to
produce a bluish product
Figure insert

ÇH,OH OH CHO
HO. OH
[H]
FeCl,. [H]
-3H,0
Ribose Furfural ÇH, 2H,0
(Pentose sugar) H, CH,
HÍ OH
Orcinol

(H] +0.50,|
H,0

HO.

H3 CH,

Bluish Product

Specifically Pentose sugar gives bluish colored complex.

Allother colors indicate a negative result for pentoses.
Note: hexoses generally react to form green, red, or brown products.
5. Osazone Test

Reducing Sugars when heated with Phenyl Hydrazine,Characteristic yellow crystals of Osazone
are formed with specific shape.
Glucose,Mannose & Fructose gives same Osazone crystals, like NEEDLE SHAPED.
Maltose gives Maltosazone crystals, like SUNFLOWER SHAPED.
Lactose gives lactosazone crystals,
like TIGHT BALL or POWDER PUFF SHAPED.
6. Benedict test
Carbohydrates which has Aldehyde functional group (Not Aromatic Aldehyde) or Having alpha
hydroxy ketone gives positive Benedict Test
It is in mild Basic Medium.

CuSO, ’ Cut* + SO
2Cu** + Reducing Sugar Cu*
Cu* ’Cu,0 ppt
Glucose (Blue Red Solution) ,,Galactose (Orange Red Solution)
Maltose ( Dark Brown with Brick Red Solution),Fructose ( Dark Brown with Brick Red Solution)
Xylose ( Brick Red solution )
7. Fehling's test
All reducing Carbohydrates give Positive Fehling's test with Fehling solution.Carbohydrates which
has Aldehyde functional group (Not Aromatic Aldehyde) and alpha hydroxy carbonyl also gives
positive Fehling's test (e.g. fuctose). While Ketones give negative fehling test. During this reaction
the aldehyde group is oxidised to acid while the copper ions are reduced to red/brown precipitate
of Cu,0. This is a common test used to detect glucose in urine as positive indication of diabetes.
CuSO, Cu + SO
2Cut* + Reducing Sugar ’ Cu,0 (Red /Brown ppt)
8 Tollen's test
This test is also given by reducing sugars. Carbohydrates reacts with Tollens reagent forms a
silver mirrOr on the inner walls of the test tube. This confirms the presence of reducing sugars.
Silver ions are reduced to metallic silver.

RCHO [Ag(NHa), JoH ’ RCOOH + Ag (Silver mirror)

(ii) H*

Note : Sucrose , poly sachharides also others non reducing sugar do not give Benedict test ,
Fehling test and Tollen's Test.
9. lodine Test
The iodine test is used to test for the presence of starch. Starch turns into an intense
Deep blue' colour upon addition of aqueous solutions of the triodide anion.
 Step - 1 : Glycolysis or EMP or HMP (Completes in cvtoplasm)

Enzymes -OH + 8 ATP

CH,0,
2NADP 2NADPH, Pyruvic acid

Step-2: Kreb cycle (Completes in mitochondria)

Ch-on
- OH + 60,
Pyruvic acid
Enzymes 6CO, + 6H,0 + 30 ATP

VITAMINES
Table : Some important Vitamins, their Sources and their Deficiency Diseases
SL Name of Sources Deficiency diseases
No. Viamins
Vitamin A Fish liver oil, carrots, butter and milk Xerophthamlia (hardening of cornea of
eye) Night blindness

2
Vitamin B |Yeast, milk, green vegetables and Beri beri
(Thiamine) cereals |(loss of appetite, retarded growth)
Vitamin B Cheilosis (fissuring at corners of mouth
3
(Riboflavin)
Milk,eggwhite, liver, kidney Jand lips), digestive disorders and burning
sensation of the skin.
Vitamin B: Yeast, milk, egg yolk, cereals and
4 Convulsions
(Pyridoxine) grams
Pernicious anaemia
5 Vitamin B2 Meat, fish, egg and curd
RBC deficient in haemoglobin)
Vitamin B; Citrus fruits, amla and green leafy
6
(Ascorbic acid)|vegetables Scurvy (bleeding gums)
Rickets (bone deformities in children)
7 Vitamin D Exposure to sunlight, fish and egg yolk and osteomalacia
(soft bones and joint pain in adults)
8 VitaminE Vegatable oils like wheat germ oil, Increased fragility of RBCs and
|sunflower oil, etc. muscular weakness
Vitamin K Green leafy vegetables Increased blood clotting time
HO-CH,
NOTE: Vitamin-D,E, K,A are fat soluble vitamins. H+
HO
Vitamin-B,C are water soluble vitamins.
HO OH
A scorbic acid
(Vitam in-C)