1. Carbohydrates

2. Carbohydrates [CX(H2O)Y] are usually defined as polyhydroxy aldehydes and ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones.
Simple carbohydrates are known as sugars or saccharides (Latin saccharum, sugar) and the ending of the names of most sugars is –ose. For example:
Glucose (for the principle sugar in blood)
Fructose (for a sugar in fruits and honey)
Sucrose (for ordinary table sugar)
Maltose (for malt sugar)

3. Classification of carbohydrates
Monosaccharide (C6H12O6)
it is a simple carbohydrate, one that one attempted hydrolysis is not cleaved to smaller carbohydrates. e.g. glucose
Disaccharide on hydrolysis is cleaved to two monosaccharide, which may be the same or different. e.g. sucrose
Oligosaccharide (oligos is a Greek word that means “few”) yields 3 10 monosaccharide unit on hydrolysis. e.g. raffinose

4. Polysaccharides are hydrolyzed to more than 10 monosaccharide units
Polysaccharides are hydrolyzed to more than 10 monosaccharide units. Cellulose is a polysaccharide molecule that gives thousands of glucose molecules when completely hydrolyzed.

5. Monosaccharides Monosaccharides are classified according to:
Over 200 different monosaccharides are known.
Monosaccharides are classified according to:
The number of carbon atoms present in the molecule.
Whether they contain an aldehyde or ketone group.
A monosaccharide containing three carbon atoms is called a triose; one containing four carbon atoms is called a tetrose.
A monosaccharide containing an aldehyde group is called an aldose; one containing a keto group is called a ketose.

7. D and L Designations of Monosaccharides
The simplest monosaccharide is glyceraldehyde, which contains a stereocenter. Therefore, it exist in two enantiomeric forms.
In 1906, (+)-glyceraldehyde is designated D-(+)- glyceraldehyde and ()- glyceraldehyde is designated L-()- glyceraldehyde.
These two compounds serve as configurational standards for all monosaccharides.

8. A monosaccharide whose highest numbered stereocenter (the penultimate carbon) has the same configuration as D-(+)- glyceraldehyde is designated as a D sugar; one whose highest numbered stereocenter has the same configuration as L-()- glyceraldehyde is designated as an L sugar.
D and L designations are not related to the optical rotations of the sugars to which they are applied.
One may encounter other sugars that are D-(+)- or D-()- and ones that are L-(+)- or L-()-.

9. Structural formulas for Monosaccharides
Fisher projection
Haworth formulas
 anomer or  anomer

10. Not all carbohydrates exist in equilibrium with six-membered hemiacetal rings, in several instances the ring is five membered.
If the monosaccharide ring is six membered, the compound is called a pyranose (e.g. -D-glucopyranose ); if the ring is five membered, the compound is designated as a furanose. (e.g. -D-ribofuranose).

11. Mutarotation
The spontaneous change that takes place in the optical rotation of  and  anomers of a sugar when they are dissolved in water. The optical rotations of the sugars change until they reach the same value.
the explanation for this mutarotation lies in the existence of an equilibrium between the open-chain form of D-(+)-glucose and the  and  forms of the cyclic hemiacetals.
the concentration of open-chain D-(+)-glucose in solution at equilibrium is very small.

12. Hemiacetal: a functional group, consisting of a carbon atom bonded to an alkoxy group and to a hydroxyl group. Hemiacetals are synthesized by adding one molar equivalent of an alcohol to an aldehyde or a ketone.

13. Glycoside Formation
Carbohydrate acetals, generally, are called glycosides, and an acetal of glucose is called a glucoside.
The methyl D-glucosides have been shown to have six-membered ring, so they are properly named methyl -D-glucopyranoside and -D-glucopyranoside.
Glycosides are stable in basic solutions because they are acetals.
In acidic solutions, glycosides undergo hydrolysis to produce a sugar and an alcohol (aglycone).

14. Sugars that contain nitrogen
1. Glycosylamines
A sugar in which an amino group replaces the anomeric OH group.
Adenosine is an example of a glycosylamine that is also called a nucleoside.

15. 2. Amino sugars
A sugar in which an amino group replaces a nonanomeric OH group. e.g. D-glucosamine.
D-glucosamine can be obtained by hydrolysis of chitin, a polysaccharide found in the shells of lobsters and crabs and in the external skeletons of insects and spiders.

16. Other Reactions of Monosaccharides
1. Enolization, Tautomerization, and Isomerization
Dissolving monosaccharides in aqueous base causes them to undergo enolizations and a series of keto-enol tautomerizations that lead to isomerizations.

17. Enols are in equilibrium with an isomeric aldehyde or ketone, but are normally much less stable than aldehydes and ketones.
Enolate ion is the conjugate base of an enol. Enolate ions are stabilized by electron delocalization.
Tautomerizm is a process by which two isomers are interconverted by a movement of an atom or a group. Enolization is a form of tautomerism.

19. 2. Formation of Ethers
The hydroxyl groups of monosaccharides are more acidic than those of ordinary alcohols because the monosaccharide contains so many electronegative oxygen atoms, all of which exert electron-withdrawing inductive effects on nearby hydroxyl groups.
In aqueous NaOH, the hydroxyl groups are converted to alkoxide ions and each of these in turn, reacts with dimethyl sulfate to yield a methyl ether.

20. 3. Conversion to Esters
Treating a monosaccharide with excess acetic anhydride and a weak base (such as pyridine or sodium acetate) converts all of the hydroxyl groups, including the anomeric hydroxyl, to ester groups.

21. 4. Oxidation Reactions of Monosaccharides
A. Fehling’s solution or Benedict’s reagent
A characteristic property of an aldehyde function is its sensitivity to oxidation.
Carbohydrates that give positive tests with Fehling’s or Benedict’s reagents are termed Reducing Sugars.
Ketoses are also reducing sugars, since under the conditions of the test, ketoses equilibrate with aldoses by way of enediol intermediates, and the aldoses are oxidized by the reagents.

22. B. Bromine Water: the synthesis of aldonic acids
Bromine water is a general reagent that selectively oxidizes the CHO group to a CO2H group.

23. C. Nitric Acid Oxidation: Aldaric Acids
Dilute nitric acid – a stronger oxidizing agent than bromine water – oxidizes both the –CHO group and the terminal –CH2OH group of an aldose to –CO2H group. These dicarboxylic acids are known as aldaric acids.

24. D. Periodate oxidations: oxidative cleavage of polyhydroxy compounds
Compounds that have hydroxyl groups on adjacent atoms undergo oxidative cleavage when they are treated with aqueous periodic acid (HIO4).
In these periodate oxidations that for every CC bond broken, a CO bond is formed at each carbon.

25. When three or more –CHOH groups are contiguous, the internal ones are obtained as formic acid. For example, glycerol

26. Oxidative cleavage also takes place when an –OH group is adjacent to the carbonyl group of an aldehyde or ketone (but not that of an acid or an ester). For example, glyceraldehyde

27. Periodic acid does not cleave compounds in which the hydroxyl groups are separated by an intervening –CH2 – group, nor those in which a hydroxyl group is adjacent to an ether or acetal function.

28. 5. Reduction of Monosaccharides: Alditols
Aldoses (and ketoses) can be reduced with sodium borohydride to compounds called alditols. For example, D-glucitol (or D-sorbitol)

29. Disaccharides
Disaccharides are carbohydrates that yield two monosaccharide molecules on hydrolysis.
e.g. sucrose, lactose, maltose
Structurally, disaccharides are glycosides in which the alkoxy group attached to the anomeric carbon is derived from a second sugar molecule.

30. Sucrose Ordinary table sugar (C12H22O11)
Acid hydrolysis yields D-glucose and D-fructose.
Sucrose is a nonreducing sugar; it gives negative tests with Fehling’s solution because neither the glucose nor the fructose portion of sucrose has a hemiacetal group (both carbonyl groups are present as full acetals (i.e. as glycosides).

31. Polysaccharides
Polysaccharides, also known as glycans, consist of monosaccharides joined together by glycosidic linkages.
Polysaccharides that are polymers of a single monosaccharide are called homopolysaccharides; those made up of more than one type of monosaccharide are called heteropolysaccharides.
Homopolysaccharides are also classified on the basis of their monosaccharide units. A homopolysaccharide consisting of glucose monomeric unit is called a glucan, one consisting of galactose units is a galactan, and so on.

32. Polysaccharides
Three important polysaccharides, all of which are glucans, are starch, glycogen, and cellulose.
Starch is the principle food reserve of plant.
Glycogen functions as a carbohydrate reserve for animals.
Cellulose serves as structural material in plants.

33. Carbohydrate Antibiotics
One of the important discoveries in carbohydrate chemistry was the isolation of the carbohydrate antibiotic called streptomycin.
Streptomycin is made up of three unusual components.
The glycosidic linkage is nearly always  .