Sakshi Education
Introduction
Carbohydrates provide the most easily accessible energy source for your body. The other main sources of energy are protein and fats. Carbohydrates often termed as “Sugars” are the “Stuff of life” for most organisms. They are widely distributed in both plants and animal tissues. They are indispensable for living organisms as they serve as skeletal structures in plants and also in insects and crustaceans. They also serve as “food serves” is the storage organs of plants and in the liver and muscles of animals. In addition, they are important source of energy required for the various metabolic activities of the living organisms. Plants are considerably richer in carbohydrates in comparison to animals.
Nomenclature:
Carbohydrates are chemical compounds that contain oxygen, hydrogen, and carbon atoms, having the functional group of an aldehyde or ketone. Pure carbohydrates contain carbon, hydrogen, and oxygen atoms, in a 1:2:1 molar ratio, giving the general formula Cn(H2O)n
The simplest carbohydrates are monosaccharides, which are small straight-chain aldehydes and ketones with many hydroxyl groups added, usually one on each carbon except the functional group. Other carbohydrates are composed of monosaccharide units and break down under hydrolysis. These may be classified as disaccharides, oligosaccharides, or polysaccharides, depending on whether they have two, several, or many monosaccharide units.
Monosaccaharides
Monosaccharides are the simplest form of carbohydrates. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose, galactose, and ribose.
Monosaccharides are the building blocks of disaccharides like sucrose (common sugar) and polysaccharides (such as cellulose and starch). Further, each carbon atom that supports a hydroxyl group (except for the first and last) is chiral, giving rise to a number of isomeric forms all with the same chemical formula. For instance, galactose and glucose are both aldohexoses, but they have different chemical and physical properties.
Monosaccharides have the chemical formula (CH2O)n. Monosaccharides contain either a ketone or aldehyde functional group, and hydroxyl groups on most or all of the non-carbonyl carbon atoms. Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. Sialic acids are found widely distributed in animal tissues and in bacteria, especially in glycoproteins and gangliosides. The predominant sialic acid is N-acetylneuraminic acid (Neu5Ac). The negative charge of this chemical that is responsible for the slippery feel of saliva and mucins coating the body’s organs. Despite its role of acting as "decoy" for invading pathogens, Neu5Ac is becoming known as an agent necessary for mediating ganglioside distribution and structures in the brain. Along with involvement in preventing infections (mucous associated with mucous membranes - mouth, nose, GI, respiratory tract), Neu5Ac acts as a receptor for influenza viruses to allow attachment to mucous cells (an early step in contracting the flu).
Classification of Monosaccharides basing on having the number of carbon atoms
It is noteworthy that, except fructose, ketoses are not as common as aldoses. The suffix "oses" is kept for aldoses and suffix "uloses" is used for ketoses.
Isomerism
Isomers are of two types i.e. - Structural isomers and Stereoisomers isomers. Structural isomers have the same molecular formula but possess different structures. The difference in structures may be exhibited either in the length of carbon chain (chain isomers) or in the position of substitutent group (positional isomer) or in possessing different functional group (functional group isomer).
Stereoisomers on the other hand have the same molecular formula and the same structure but differ only in spatial configuration. The compound said to be a stereoisomer it should have atleast one asymmetric carbon atoms (excluding geometric isomers, which is a class of diastereomers).
In stereoisomers, the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes enantiomers where different isomers are mirror images of each other, and diastereomers (stereoisomers that are not non-superimposable, non –mirror images; have different physical properties) when they are not. Diastereomerism is again subdivided into conformational isomerism (conformers) when isomers can interconvert by chemical bond rotations and cis-trans isomerism (also known as geometrical isomerism) when this is not possible. Note that although conformers can be referred to as having a diastereomeric relationship, the isomers over all are not diastereomers, since bonds in conformers can be rotated to make them mirror images.
There are several conventions used for naming chiral compounds, all displayed as a prefix before the chemical name of the substance:
Epimerism
In chemistry, an epimer is a stereoisomer that has a different configuration at only one of several chiral carbon centers. When an epimer becomes in incorporated into a ring structure it is called an anomer. For example, the sugars a-glucose and ß-glucose are epimers. In the a-glucose, the -OH group on the first (anomeric) carbon is in the direction opposite the methyl group. In the ß-glucose, the -OH group is oriented in the same direction as the methyl group. Biologically the most important epimers of glucose are mannose and galactose formed by epimerization of C-2 and C-4 respectively. In body epimerization is catalyzed by epimerase.
Sugar derivatives: Various derivatives of sugars exist including -
Sugar alcohol - Lacks an aldehyde or ketone. An example is ribitol.
Sugar acid - The aldehyde at C1, or the hydroxyl on the terminal carbon, is oxidized to a carboxylic acid. Examples are gluconic acid and glucuronic acid.
Amino sugar - An amino group substitutes for one of the hydroxyls. An example is glucosamine. The amino group may be acetylated. N-acetylneuraminate, (N-acetylneuraminic acid, also called sialic acid) is often found as a terminal residue of oligosaccharide chains of glycoproteins. Sialic acid imparts negative charge to glycoproteins, because its carboxyl group tends to dissociate a proton at physiological pH
Important properties of monosaccharides:
Physical Properties: Monosaccharides are colorless, crystalline solids and because H bonding is possible, they are soluble in water and insoluble in nonpolar solvents.
Chemical properties:
Intramolecular Cyclization:
Most monosaccharides form cyclic structures, which predominate in aqueous solution, by forming hemiacetals or hemiketals (depending on whether they are aldoses or ketoses) with themselves. Glucose, for example, forms a hemiacetal linkage between its carbon-1 and the hydroxyl group of its carbon-5. Since such a reaction introduces an additional chiral center, two anomers are formed from each distinct straight-chain monosaccharide. The interconversion between these two forms is called mutarotation.
Mutarotation is the change in specific rotation that accompanies the equilibrium of a and b anomers in aqueous solution. For example, a solution prepared by dissolving crystalline a-D glucopyranose in water has a specific rotation of +112, which gradually decreases to an equilibrium value of +52.7 as a-D glucopyranose reaches equilibrium with b–D- glucopyranose.
Formation of Glycosides: Name the resulting glycoside by listing the alkyl or aryl group bonded to oxygen, followed by the name of the carbohydrate in which the ending –e is replaced by –ide. Sugars acetals are called glycosides and the acetal bond is called the glycosidic bond.
Acetals = Hemiacetal + Alcohol
Reduction to Alditols: The carbonyl group can be reduced to an hydroxyl group by a variety of reducing agents. The reduction products are known as alditols. Name alditols by dropping the –ose from the name of the monosaccharide and add –itol. Reduction of a aldose forms one alditol. Reduction of a ketose forms two alditols because the reaction creates a new asymmetric carbon in the product. D-Mannitol, the alditol formed from the reduction of D-mannose, is found in muschrooms, olives, and onions. The reduction of D-fructose forms D-mannitol and D-glucitol, the C-2 epimer of D-mannitol. D-Glucitol – also called sorbitol – is about 60% as sweet as sucrose. It is found in plums, pears, cherries, and berries and is used as a sugar substitute in the manufacture of candy.
D-Glucitol is also obtained from the reduction of either D-glucose or L-glucose. D-Xylitol obtained from the reduction of D-xylose - is used as a sweetening agent in cereals and sugarless gum.
Oxidation to Aldonic Acids (reducing sugars)
Several agents including oxygen oxidize aldehydes to carboxylic acids. Any carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing sugar (it reduces the oxidizing agent). Aldehydes can be distinguished from ketoses by observing what happens to the color of an aqueous soulution of bromine when it is added to the sugar. If a small amount of an aqueous solution of Br2 (Oxidizing agent) is added to an unknown monosaccharide, the reddish Br2 will disappear if the monosaccharide is an aldose, but will persist if the monosaccharide is a ketose.
Glucose with mild oxidizing agents form gluconic acid, strong oxidizing agent (HNO3) forms glucaric acid (in which both the aldehyde and primary alcoholic function will be oxidized).
Both aldoses and ketoses are oxidized to aldonic acids by Tollen’s reagent (Ag+, NH3, OH-) so that reagent cannot be used to distinguish between aldoses and keoses, but it would be useful to distinguish aldehydes and ketones(Tollens reagent oxidizes aldehydes but not ketones).
Metal hydroxides like CU (OH2) (Benedict’s and Fehlings test), oxidize the aldehydes and ketones of mono and disaccharides and are at the same themselves reducing to the lower oxides or to free metals.
Reducing sugar + 2Cu++
2Cu+ + 2OH-
Oxidised sugar + 2Cu+
Cu2O + H2O
For many years, this test is used to detect and measure elevated glucose levels in blood and urine in the diagnosis of diabetes mellitus. Now more sensitive methods for measuring blood glucose employ an enzyme.
Glucose + O2
Glucose Oxidase
D-Glucono-delta lactone +H2O2
H202 + Colourless compound
Peroxidase
Colour compound
Oxidation to Uronic Acids
Enzyme-catalyzed oxidation of the primary alcohol at carbon 6 of a hexose yields an uronic acid. D- glucuronic acid is widely distributed in both the plant and animal worlds. In humans, it serves as an important component of the acidic polysaccharides of connective tissues. The body also uses it to detoxify foreign phenols and alcohols. In the liver, these compounds are converted to glycosides of glucuronic acid and then excreted in the urine. The intravenous anesthetic propfol is converted to the following glucuronide and excreted in urine.
Phosphoric Esters: Mono and diphosphoric esters are important intermediates in the metabolism of monosaccharides. Phosphoric acid is a strong enough acid so that at the pH of cellular and intercellular fluids, both acidic protons of a phosphoric ester are ionized, giving the ester a charge of -2.
Reaction with acids: By contrast monosaccharides are generally stable in dilute mineral acids even on heating, when hexoses are heated with strong mineral acids, however they are dehydrated and hydroxy methyl furfurol is formed Pentoses are dehydrated to furfural.. This dehydration reaction is the basis of certain qualitative tests (Molisch’s test) for sugars, since the furfurols can be reacted with a-napthol and the aromatic compounds to form characteristic coloured compounds.
Reaction with alkali: The conversion of glucose to fructose and mannose in dilute alkali by enolization adjacent to the carbonyl group to form an enediol, a reaction analogous to certain biochemical transformations. This reaction is known as Lobry de bruyn-van ekenstein transformation
Osazone test: The osazone reaction was developed and used by Emil Fischer to identify aldose sugars differing in configuration only at the alpha-carbon. The upper equation shows the general form of the osazone reaction, which affects an alpha-carbon oxidation with formation of a bis-phenylhydrazone, known as an osazone.
Because the configuration of number-2 carbon is lost during osazone formation, C-2 epimers form identical osazones. For example, D-idose and D-gulose, which are C-2 epimers, both form the same osazone.
The number –1 and number –2 carbons of ketoses react with phenylhydrazine, too. Consequently, D-fructose, D-glucose, and D-mannose all form the same osazone.
The times required for the formation of the osazones can be a valuable aid in distinguishing among various sugars.
Glucose -5min - Broom stick
Fructose -2min - Broom stick
Galactose -2min - Rhombic like
Lactose -10-12min - Powder Puff
Maltose -10-15min- Sunflower
Chain Shortening and Lengthening
These two procedures permit an aldose of a given size to be related to homologous smaller and larger aldoses. Thus Ruff degradation of the pentose arabinose gives the tetrose erythrose. Working in the opposite direction, a Kiliani-Fischer synthesis applied to arabinose gives a mixture of glucose and mannose.
Carbohydrates provide the most easily accessible energy source for your body. The other main sources of energy are protein and fats. Carbohydrates often termed as “Sugars” are the “Stuff of life” for most organisms. They are widely distributed in both plants and animal tissues. They are indispensable for living organisms as they serve as skeletal structures in plants and also in insects and crustaceans. They also serve as “food serves” is the storage organs of plants and in the liver and muscles of animals. In addition, they are important source of energy required for the various metabolic activities of the living organisms. Plants are considerably richer in carbohydrates in comparison to animals.
Nomenclature:
Carbohydrates are chemical compounds that contain oxygen, hydrogen, and carbon atoms, having the functional group of an aldehyde or ketone. Pure carbohydrates contain carbon, hydrogen, and oxygen atoms, in a 1:2:1 molar ratio, giving the general formula Cn(H2O)n
The simplest carbohydrates are monosaccharides, which are small straight-chain aldehydes and ketones with many hydroxyl groups added, usually one on each carbon except the functional group. Other carbohydrates are composed of monosaccharide units and break down under hydrolysis. These may be classified as disaccharides, oligosaccharides, or polysaccharides, depending on whether they have two, several, or many monosaccharide units.
Monosaccaharides
Monosaccharides are the simplest form of carbohydrates. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose, galactose, and ribose.
Monosaccharides are the building blocks of disaccharides like sucrose (common sugar) and polysaccharides (such as cellulose and starch). Further, each carbon atom that supports a hydroxyl group (except for the first and last) is chiral, giving rise to a number of isomeric forms all with the same chemical formula. For instance, galactose and glucose are both aldohexoses, but they have different chemical and physical properties.
Monosaccharides have the chemical formula (CH2O)n. Monosaccharides contain either a ketone or aldehyde functional group, and hydroxyl groups on most or all of the non-carbonyl carbon atoms. Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. Sialic acids are found widely distributed in animal tissues and in bacteria, especially in glycoproteins and gangliosides. The predominant sialic acid is N-acetylneuraminic acid (Neu5Ac). The negative charge of this chemical that is responsible for the slippery feel of saliva and mucins coating the body’s organs. Despite its role of acting as "decoy" for invading pathogens, Neu5Ac is becoming known as an agent necessary for mediating ganglioside distribution and structures in the brain. Along with involvement in preventing infections (mucous associated with mucous membranes - mouth, nose, GI, respiratory tract), Neu5Ac acts as a receptor for influenza viruses to allow attachment to mucous cells (an early step in contracting the flu).
Classification of Monosaccharides basing on having the number of carbon atoms
| Name (Carbon Atoms) | Formula | Aldoses | Ketoses |
| Monoses | C1H201 | Formaldehyde |
|
| Diose: | C2H4O2 | Glycoaldehyde |
|
| Triose | C3H6O3 | Glyceraldehyde or Glycerose | Dihydroxy acetone |
| Tetroses | C4H8O4 | Erythrose and Threose | Erythrulose |
| Pentoses | C5H10O5 | Ribose, Arabinose, Xylose and Lyxose | Ribulose and Xylulose |
| Hexoses | C6H12O6 | Allose, Altrose, Galctose, Glucose, Gulose, Idose, Mannose and Talose | Fructose, Psicose, Sorbose and Tagatose |
| Heptoses | C7H14O7 |
| Mannoheptulose and Sedoheptulose |
| Nanoses | C9H18O9 | Sialic acid (N-acetylneuraminic acid (Neu5Ac) | |
It is noteworthy that, except fructose, ketoses are not as common as aldoses. The suffix "oses" is kept for aldoses and suffix "uloses" is used for ketoses.
Isomerism
Isomers are of two types i.e. - Structural isomers and Stereoisomers isomers. Structural isomers have the same molecular formula but possess different structures. The difference in structures may be exhibited either in the length of carbon chain (chain isomers) or in the position of substitutent group (positional isomer) or in possessing different functional group (functional group isomer).
Stereoisomers on the other hand have the same molecular formula and the same structure but differ only in spatial configuration. The compound said to be a stereoisomer it should have atleast one asymmetric carbon atoms (excluding geometric isomers, which is a class of diastereomers).
In stereoisomers, the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes enantiomers where different isomers are mirror images of each other, and diastereomers (stereoisomers that are not non-superimposable, non –mirror images; have different physical properties) when they are not. Diastereomerism is again subdivided into conformational isomerism (conformers) when isomers can interconvert by chemical bond rotations and cis-trans isomerism (also known as geometrical isomerism) when this is not possible. Note that although conformers can be referred to as having a diastereomeric relationship, the isomers over all are not diastereomers, since bonds in conformers can be rotated to make them mirror images.
There are several conventions used for naming chiral compounds, all displayed as a prefix before the chemical name of the substance:
- (+) Vs (-) also written d- vs. l-
Based on the substance's ability to rotate polarized light.
- D- vs. L-
Based on the actual geometry of each enantiomer, with the version synthesized from naturally occurring (+)-glyceraldehyde being considered the D- form.
- (R)- vs. (S)-
Based on the actual geometry of each enantiomer, using the Cahn-Ingold-Prelog priority rules to classify the form. Molecules with multiple chiral centers will have a corresponding number of letters; e.g. natural d-alpha-tocoperol is R,R,R-alpha-tocoperol.
The (+)- vs. (-)- convention is the only one based on optical properties. The other two conventions are based on the actual geometry of each enantiomer. There is no correspondence between any convention. In nature, many chiral substances are only produced in one optical form, while (most) man-made chiral substances are racemic mixtures (optical activity is zero). The purity of enantiomers can be determined by optical rotation
The maximum number of stereoisomers is based on the number of chiral centers a compound has.
Epimerism
In chemistry, an epimer is a stereoisomer that has a different configuration at only one of several chiral carbon centers. When an epimer becomes in incorporated into a ring structure it is called an anomer. For example, the sugars a-glucose and ß-glucose are epimers. In the a-glucose, the -OH group on the first (anomeric) carbon is in the direction opposite the methyl group. In the ß-glucose, the -OH group is oriented in the same direction as the methyl group. Biologically the most important epimers of glucose are mannose and galactose formed by epimerization of C-2 and C-4 respectively. In body epimerization is catalyzed by epimerase.
Sugar derivatives: Various derivatives of sugars exist including -
Sugar alcohol - Lacks an aldehyde or ketone. An example is ribitol.
Sugar acid - The aldehyde at C1, or the hydroxyl on the terminal carbon, is oxidized to a carboxylic acid. Examples are gluconic acid and glucuronic acid.
Amino sugar - An amino group substitutes for one of the hydroxyls. An example is glucosamine. The amino group may be acetylated. N-acetylneuraminate, (N-acetylneuraminic acid, also called sialic acid) is often found as a terminal residue of oligosaccharide chains of glycoproteins. Sialic acid imparts negative charge to glycoproteins, because its carboxyl group tends to dissociate a proton at physiological pH
Important properties of monosaccharides:
Physical Properties: Monosaccharides are colorless, crystalline solids and because H bonding is possible, they are soluble in water and insoluble in nonpolar solvents.
Chemical properties:
Intramolecular Cyclization:
Most monosaccharides form cyclic structures, which predominate in aqueous solution, by forming hemiacetals or hemiketals (depending on whether they are aldoses or ketoses) with themselves. Glucose, for example, forms a hemiacetal linkage between its carbon-1 and the hydroxyl group of its carbon-5. Since such a reaction introduces an additional chiral center, two anomers are formed from each distinct straight-chain monosaccharide. The interconversion between these two forms is called mutarotation. Mutarotation is the change in specific rotation that accompanies the equilibrium of a and b anomers in aqueous solution. For example, a solution prepared by dissolving crystalline a-D glucopyranose in water has a specific rotation of +112, which gradually decreases to an equilibrium value of +52.7 as a-D glucopyranose reaches equilibrium with b–D- glucopyranose. Formation of Glycosides: Name the resulting glycoside by listing the alkyl or aryl group bonded to oxygen, followed by the name of the carbohydrate in which the ending –e is replaced by –ide. Sugars acetals are called glycosides and the acetal bond is called the glycosidic bond. Acetals = Hemiacetal + Alcohol
Reduction to Alditols: The carbonyl group can be reduced to an hydroxyl group by a variety of reducing agents. The reduction products are known as alditols. Name alditols by dropping the –ose from the name of the monosaccharide and add –itol. Reduction of a aldose forms one alditol. Reduction of a ketose forms two alditols because the reaction creates a new asymmetric carbon in the product. D-Mannitol, the alditol formed from the reduction of D-mannose, is found in muschrooms, olives, and onions. The reduction of D-fructose forms D-mannitol and D-glucitol, the C-2 epimer of D-mannitol. D-Glucitol – also called sorbitol – is about 60% as sweet as sucrose. It is found in plums, pears, cherries, and berries and is used as a sugar substitute in the manufacture of candy. D-Glucitol is also obtained from the reduction of either D-glucose or L-glucose. D-Xylitol obtained from the reduction of D-xylose - is used as a sweetening agent in cereals and sugarless gum.
Oxidation to Aldonic Acids (reducing sugars)
Several agents including oxygen oxidize aldehydes to carboxylic acids. Any carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing sugar (it reduces the oxidizing agent). Aldehydes can be distinguished from ketoses by observing what happens to the color of an aqueous soulution of bromine when it is added to the sugar. If a small amount of an aqueous solution of Br2 (Oxidizing agent) is added to an unknown monosaccharide, the reddish Br2 will disappear if the monosaccharide is an aldose, but will persist if the monosaccharide is a ketose. Glucose with mild oxidizing agents form gluconic acid, strong oxidizing agent (HNO3) forms glucaric acid (in which both the aldehyde and primary alcoholic function will be oxidized).Both aldoses and ketoses are oxidized to aldonic acids by Tollen’s reagent (Ag+, NH3, OH-) so that reagent cannot be used to distinguish between aldoses and keoses, but it would be useful to distinguish aldehydes and ketones(Tollens reagent oxidizes aldehydes but not ketones).
Metal hydroxides like CU (OH2) (Benedict’s and Fehlings test), oxidize the aldehydes and ketones of mono and disaccharides and are at the same themselves reducing to the lower oxides or to free metals.
Reducing sugar + 2Cu++
2Cu+ + 2OH-
Oxidised sugar + 2Cu+
Cu2O + H2O
For many years, this test is used to detect and measure elevated glucose levels in blood and urine in the diagnosis of diabetes mellitus. Now more sensitive methods for measuring blood glucose employ an enzyme.
Glucose + O2
Glucose Oxidase
D-Glucono-delta lactone +H2O2
H202 + Colourless compound
Peroxidase
Colour compound
Oxidation to Uronic Acids
Enzyme-catalyzed oxidation of the primary alcohol at carbon 6 of a hexose yields an uronic acid. D- glucuronic acid is widely distributed in both the plant and animal worlds. In humans, it serves as an important component of the acidic polysaccharides of connective tissues. The body also uses it to detoxify foreign phenols and alcohols. In the liver, these compounds are converted to glycosides of glucuronic acid and then excreted in the urine. The intravenous anesthetic propfol is converted to the following glucuronide and excreted in urine.
Phosphoric Esters: Mono and diphosphoric esters are important intermediates in the metabolism of monosaccharides. Phosphoric acid is a strong enough acid so that at the pH of cellular and intercellular fluids, both acidic protons of a phosphoric ester are ionized, giving the ester a charge of -2.
Reaction with acids: By contrast monosaccharides are generally stable in dilute mineral acids even on heating, when hexoses are heated with strong mineral acids, however they are dehydrated and hydroxy methyl furfurol is formed Pentoses are dehydrated to furfural.. This dehydration reaction is the basis of certain qualitative tests (Molisch’s test) for sugars, since the furfurols can be reacted with a-napthol and the aromatic compounds to form characteristic coloured compounds.
- C5H10O5 (pentose) + (conc.) H2SO4 C5H4O2 + 3 H2O
- C5H4O2 (furfural) + 2 C10H8OH (a-naphthol) Colored product
Reaction with alkali: The conversion of glucose to fructose and mannose in dilute alkali by enolization adjacent to the carbonyl group to form an enediol, a reaction analogous to certain biochemical transformations. This reaction is known as Lobry de bruyn-van ekenstein transformation Osazone test: The osazone reaction was developed and used by Emil Fischer to identify aldose sugars differing in configuration only at the alpha-carbon. The upper equation shows the general form of the osazone reaction, which affects an alpha-carbon oxidation with formation of a bis-phenylhydrazone, known as an osazone. Because the configuration of number-2 carbon is lost during osazone formation, C-2 epimers form identical osazones. For example, D-idose and D-gulose, which are C-2 epimers, both form the same osazone. The number –1 and number –2 carbons of ketoses react with phenylhydrazine, too. Consequently, D-fructose, D-glucose, and D-mannose all form the same osazone.
The times required for the formation of the osazones can be a valuable aid in distinguishing among various sugars.
Glucose -5min - Broom stick
Fructose -2min - Broom stick
Galactose -2min - Rhombic like
Lactose -10-12min - Powder Puff
Maltose -10-15min- Sunflower
Chain Shortening and Lengthening
These two procedures permit an aldose of a given size to be related to homologous smaller and larger aldoses. Thus Ruff degradation of the pentose arabinose gives the tetrose erythrose. Working in the opposite direction, a Kiliani-Fischer synthesis applied to arabinose gives a mixture of glucose and mannose.Published date : 17 May 2014 05:20PM
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