Carbohydrates sem 3 bsc

Introduction:
• The carbohydrates are the most important naturally occurring
organic substances.
• These classes of natural products are important biologically and
essential to sustain life.
• They are wide spread in animals and plants.
• The dry weight of plants is typically composed of 55% to 80% of
polymetric carbohydrate cellulose along with relatd structural
materials.
• These along with fats, proteins, forms the basis of animal nutrition.
• Sugars, starches, cellulose are best known members of this group.
BY- Ms MAYURI R SOMPURA 2

Introduction:
• Carbohydrate moieties also occur in a number of complex materials
such as:
I. glycosides
II. Mucoproteins
III. Nucleicacids
Carbohydrates are only composed of carbon, hydrogen and
oxygen.
General formula - CX(H2O)Y
C6H12O6 Or C6(H2O)6 / C12H22O11 Or C12(H2O)11
They appear to be hydrates of carbon.

Introduction:
• Carbohydrates are formed in plants by photosynthesis from carbon
dioxide and water.
• This fundamental principle in life is catalyzed by the green plant
pigment- chlorophyll , Enzyme systems & oxygen.
• nCO2 + nH2O → (CH2O)n + nO2
• 6CO2 + 6H2O → (CH2O)6 + 6O2

Introduction:
• We come across carbohydrates at almost every turn in our daily
lives.
• The paper is largely composed of cellulose.
• The flour from which we prepare bread is largely composed of
starch.
• Starch is also a major constituent of many other food stuffs such as
potatoes, rice, beans, corn, peas.

Introduction:
• Carbohydrates are white solids, sparingly soluble in organic liquids
except for some polysaccharides, soluble in water.
• Many carbohydrates of low molecular weight have sweet taste.

Classification of carbohydrates:
• Carbohydrates are classified into 4 major classes depending upon
whether or not they undergo hydrolysis.
• If they do undergo hydrolysis, what are the number of products
formed.

(a) monosaccharides:
• These are the simplest from of Carbohydrates.
• They are also called as ‘simple sugars’.
• They cannot be further hydrolyzed.
• The most important of them are pentoses (CH2O)5 and hexoses
(CH2O)6.
• General formula - (CH2O)n

(a) monosaccharides:
• The monosaccharaides are further sub-divided in terms of number
of carbons and nature of carbonyl group present in the molecule.
• Aldehyde group – aldose
• Ketone group – ketose
• A three carbon chain is called – aldotriose or ketotriose.
• A four carbon chain is called – aldotetrose and ketotetrose
• And so on..

(b) oligosaccharides:
• The carbohydrates that hydrolyze to yield 2-10 molecules of a
monosaccharaide is known as oligosaccharide.
• General formula – Cn(H2O)n-1
• Carbohydrates that undergo hydrolysis to produce only two
molecules of monosaccharide is known as a disaccharide.
• Eg,
• sucrose & maltose – same molecular formula - C12(H2O)11
• But raffinose is hydrolyzed to give three moles of a
monosaccharide and hence is called a trisaccharide.

(c) polysaccharides:
• These are composed of several monosaccharide units are polymers
on hydrolysis.
• They yield a large number i.e. > 10 of monosaccharides.
• Eg,
• starch and cellulose (glucose polymer)
• These are non-sugars, insoluble in water and are most abundant
form of carbohydrates.

Nomenclature:
•
Aldehyde group present in carbohydrates :-
Aldo triose Having 3 carbons
Aldo tetrose Having 4 carbons
Aldo pentose Having 5 carbons
Aldo hexose Having 6 carbons
Ketone group present in carbohydrates :-
Aldo triose Having 3 carbons
Aldo tetrose Having 4 carbons
Aldo pentose Having 5 carbons
Aldo hexose Having 6 carbons

General reactions of monosaccharides:
• Monosaccharides are aldehyde and ketone derivative of higher polyhydric
alcohols, they give most, but not all, of the characteristic reaction of arbonyl
group as well as the alcoholic group.
• In addition to these relationships they also gove rise to some special reactions
due to the presence of a carbonyl and alcoholic group in the same molecule..
Osazone formation :-
• Glucose and fructose react with phenylhydrazine to form same osazones.
• 3 moles of phenylhydrazines are consumed in aldoses as well as in ketoses to
form osazones, aniline and ammonia.

(a) Osazone formation :
• According to Fisher’s mechanism, glucose reacts first with phenyl hydrazine
molecule with the carbonyl group of aldehyde of aldose to form
phenylhydrazone.
• The second ,molecule of phenylhydrazine oxidises the C-2 hydroxyl group of
phenylhydrazone to carbonyl group and is itself reduced to aniline and
ammonia.
• Finally the newly deve;loped carbonyl group reacts with the third molecule of
phenylhydrazine to form phenylosazone.
• These three steps summarized in case of glucose molecule.

(a) Osazone formation :
• A phenylhydrazine molecule reacts with carbonyl group at C-2 to from
phenylhydrazone.
• Then second molecule of phenylhydrazine oxides the C-1 hydroxyl group of
phenylhydrazone to a carbonyl group and is itself reduced to aniline and
ammonia.
• Finally the newly formed carbonyl group reacts with the third molecule of
phenylhydrazine to form osazone.

(b)oxidation:
1. Oxidation with bromine water.
2. Oxidation with nitric acid
3. Oxidation with periodic acid
4. Oxidation with Fehling solution/ tollens reagent/ Benedict reagent

(1)Oxidation with bromine water:
• Bromine water is mildly acidic solution (PH=6.0) .
• When they react with glucose, glucose oxidises the –CHO group to –COOH
group.
• Aldose → Aldonic acid (gluconic acid)
• Bromine water donot react with fructose as it doesnot have an aldehyde group.

(2)Oxidation with nitric acid:
• When glucose is oxidised with nitric acid to yield dicarboxylic acids kown as
aldaric acid (saccharic acid).
• Primary alcoholic group at C-6 position and –CHO at C-1 position will be
oxidized to yield –COOH group.
• Fructose can be oxidized with nitric acid.
• Fructose is converted into mixture of three acids.
• Hence this gives the evidence of the presence of C=O group in fructose
molecule.

(3)Oxidation with periodic acid:
• Oxidation of periodic acid shows that 5 moles of HIO4 is used.
• After the oxidation reaction 5 moles of formic acid and one mole of
formaldehyde are obtained.
• Fructose is oxidized with periodic acid to obtain:
2 moles – formaldehyde
1 mole - glycolic acid
3 moles – formic acid

(4)Oxidation with reagents:
Sr.no Reagent name Chemical formation of reagent
1 Fehling’s reagent Fehling’s reagent A – Copper sulphate solution
Fehling’s reagent B – Sodium hydroxide +
Sodium Potassium Tartrate
2 Benedict’s
reagent
Copper sulphate + Sodium carbonate + Sodium
citrate
3 Tollen’s reagent Silver nitrate + Sodium hydroxide + Ammonium
hydroxide

(4)Oxidation with reagents:
• Gluocse and fructose react with Fehling’s or Benedict’s reagent to
produce the precipitate of Cu2O.
• Glucose is oxidized and converted into gluconic acid.
• Fructose id oxidized and converted into glycolid and tartaric acid.
• With tollen’s – glucose and fructose give the same reaction and
produces silver.
• Glucose is converted to gluconic acid that means it has –CHO group.
• Fructose is oxidized and fragmented.
• Glycolic acid and tartaric acid are produced that means fructose has
C=O group.

(b) Reduction :
• Gluocse reacts with Na-Hg amalgam in aqueous solution, the glucose
is reduced and converted to hexahydroxy alcohol (sorbitol).
• Fructose is reduced by electric reduction method in presence of acidic
medium and alkali medium converted into sorbitol and mannitol.
• Epimers - are optical isomers which differ only in the configuration
of one asymmetric center.
• Sorbitol and mannitol are epimers.

(b) Reduction :
• On reduction with red phosphorous and hydroiodic acid at 100℃
temperatire yield sorbitol ( + mannitol for fructose ) which again
reacts with same to form 2-iodohexane .
• 2-iodohexane is further heated for a long time to get n-hexane.
• Which means glucose and fructose molecule structure is in a single
chain.

(C) ACETYLATION :
• On acetylation, glucose and fructose yield ester derivatives.
• Acetylated penta acetyl derivatives are formed.
• Which means they both hsve 5 –OH groups present in their structure.

Carbohydrates sem 3 bsc

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Carbohydrates sem 3 bsc