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Organic Chemistry II
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Carbohydrates
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Introduction
The body get its energy from three main classes of food : 1. Carbohydrates ( consider the most
important source of energy ) 2. Protein 3. Fat
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Introduction
Carbohydrates : Polyhydroxy aldehyde or polyhydroxy ketone The common chemical formula for carbohydrates is Cn(H2O)n the ratios are usually:
1 Carbon: 2 Hydrogens: 1 Oxygen
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Classification of Carbohydrates
Carbohydrates Di-saccharide
Poly-saccharide
Oligo-saccharide
Mono-saccharide
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Classification of Carbohydrates ,cont.
A. monosaccharide: The basic unite of carbohydrate is the monosaccharide's contain a single polyhydroxy aldehyde or ketone unit E.g.: glucose, fructose.
•Glucose is aldohexose •Fructose is ketohexose
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Classification of Carbohydrates ,cont.
A. monosaccharide: Aldohexose: hexose is a monosaccharide with six carbon atoms, having the chemical formula “C6H12O6”. An aldohexose is a hexose with an aldehyde group on one end.
ketohexose: is a ketone-containing hexose (a six-carbon monosaccharide).
Classification of Carbohydrates ,cont.
Glucose Fructose
Keto- group
aldehyde- group
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Classification of Carbohydrates ,cont.
A. monosaccharide: Glucopyranose : cyclic form of glucose containing a pyranose ring. Pyranose ring : is a collective term for carbohydrates that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom.
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Classification of Carbohydrates ,cont.
hemiacetal group -C(OH)H-O-.
form from the open-chain reaction between the aldehyde group -(C=O)H at C-1, and the hydroxyl group -OH at C-4 or C-5.
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Classification of Carbohydrates ,cont.
B. Disaccharides : Disaccharides consist of two monosaccharide units linked together by a covalent bond Example of disaccharide : 1) Lactose ( milk sugar)= galactose +glucose
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Classification of Carbohydrates ,cont.
1) Lactose
Lactose intolerance: is the inability to metabolize lactose, because of a
lack of the required enzyme lactase in the digestive system.
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2) Maltose (malt sugar)= Glucose + Glucose
Classification of Carbohydrates ,cont.
Classification of Carbohydrates ,cont.
3) Sucrose ( table sugar) =
glucose + fructose
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Classification of Carbohydrates ,cont.
C. Oligosaccharides: contain from 3 to 10 monosaccharide units E.g. : Raffinose (trisaccharide)=
galactose+ fructose+ glucose
D. Polysaccharides: contain very long chains of hundreds or thousands of monosaccharide units E.g. : cellulose, glycogen, starch.
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Physical properties
A. Monosaccharide :
Most monosaccharide's have a sweet taste (fructose is sweetest; 73% sweeter than sucrose).
They are crystalline solids at room temperature.
They are extremely soluble in water
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B. Disaccharide These are crystalline, water-soluble, sweet taste. It is a white, odorless
Physical properties
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C. Polysaccharide :
starch is a white, tasteless and odorless powder
Starches are usually insoluble in water because
of the high molecular weight, but they can form
thick colloidal suspensions with water. (Absorb
water but do not dissolve in water)
Physical properties
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Physical properties
lactose Fructose
Powder Crystalline State
White Color
Sweet
Sweet
73% sweeter than sucrose
Test
Flammable Flammability
Soluble in H2O
Extremely
soluble in H2O Solubility
neutral Effect on L.P
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Physical properties
Starch Sucrose Maltose
powder Crystalline Crystalline State
white Color
tasteless Sweet test Test
Flammable Flammability
Insoluble in H2O
Soluble in H2O
Solubility
neutral Effect on L.P
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Chemical Properties
Chemical tests
General tests
Molisch’s
test
Oxidation test
Fehlig test
Benedict’s test
Tollens’ test
Barfoed's Test
Specific tests
Seliwanoff's Test
Iodine solution test
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Chemical Properties , cont.
General test:
Molisch’s test
Use to distinguish between carbohydrates and non-carbohydrates
procedure: 1 ml of carbohydrate solution + 3 drops Molisch reagent +1 ml conc.H2SO4 (carefully added on the wall of tube)
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Chemical Properties , cont.
General test:
Molisch’s test
Result: a purple ring forming at the interface between the denser sulfuric acid and the less dense test solution above .
Chemical Properties , cont.
Molisch’s test
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Chemical Properties , cont.
Oxidation tests:
1) Fehling test
procedure: few mg of carbohydrates + 2 ml of Fehling reagent A&B then warm in water
bath for 2.
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Chemical Properties , cont.
Oxidation tests:
1) Fehling test
Result :
change in blue color
All carbohydrates give +ve result except sucrose & starch
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Chemical Properties , cont.
Fehling test
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Chemical Properties , cont.
Oxidation tests: 2) Benedict’s test
procedure: 2ml of carbohydrates + 2ml of Bendict’s soultion then warm in water bath for 2-3 min.
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Chemical Properties , cont.
Oxidation tests: 2) Benedict’s test
Result :
Increasing amount of reduction of the sugar
Green ,orang, red ,brown
All carbohydrates give +ve except sucrose &
starch
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Chemical Properties , cont.
Benedict’s test
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Chemical Properties , cont.
Oxidation tests:
3) Tollens’ silver mirror test
procedure: 1 ml of carbohydrates+ 1 ml of Tollens’ reagent ;then warm in water bath for 2-5 min.
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Chemical Properties , cont.
Oxidation tests:
3) Tollens’ silver mirror test
Result:
make silver mirror
Except sucrose & starch
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Chemical Properties , cont.
Tollens’ silver mirror test:
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Chemical Properties , cont.
Oxidation tests: 4) Barfoed's Test
To differentiate between mono- & disaccharide
procedure: 1ml of carbohydrates +3ml of Barfoed's reagent. The solution is then heated in a boiling water bath for 3-10min.
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Chemical Properties , cont.
Oxidation tests: 4) Barfoed's Test
Result : formation of a reddish precipitate within
three minutes. +ve fructose -ve starch, sucrose , maltose & lactose
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Chemical Properties , cont.
Barfoed's Test
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Chemical Properties , cont.
Specific tests for ketones sugar :
Seliwanoff's Test
Procedure: 1ml of carbohydrates +2 ml of Seliwanoff's reagent (a solution of resorcinol and HCl). The solution is then heated in a boiling water bath for 3-6 min.
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Chemical Properties , cont.
Specific tests for ketones sugar :
Seliwanoff's Test Reuslt : Give red color +ve fructose & sucrose
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Chemical Properties , cont.
Seliwanoff's Test
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Chemical Properties , cont.
Specific tests:
Iodine solution test
Producer : few mg of starch + 1ml of iodine solution
Result:
A dark blue color
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Chemical Properties , cont.
Iodine solution test
Thank you