Carbohydrates are a molecule made up of Carbon, Hydrogen and Oxygen only. It is a group which includes sugars, starch and cellulose. They are known as saccharides in terms of biochemistry. There are four types of saccharides: monosaccharides, disaccharides, oligosaccharides and polysaccharides.
They are nutritional molecules and are found in a variety of foods. Examples of carbohydrates include glucose, lactose, cellulose, etc.
Structurally a carbohydrate confers to the formula (CH2O)n. However, not all carbohydrates follow it. It has an aldehyde or ketone as a functional group.
Let us look at the reactions a carbohydrate can undergo:
1. Alkylation
Carbohydrates go through a SN2 reaction to produce ethers. They react with alkylating agents such as diazomethane or alkyl iodide and with benzyl halides for benzylation.
2. Acylation
It is a nucleophilic acyl substitution reaction where the -OH group reacts with the acylating agents such as acyl anhydrides or acyl halides to give esters.
3. Reduction
It is a nucleophilic addition reaction where the C=O group is reduced to alcohols by sodium borohydride. The resulting product is known as alditols.
If the carbohydrate is an aldehyde, it is reduced to primary alcohol, but if it is a ketose, it forms secondary alcohol.
4. Oxidation
Sugars readily undergo oxidation to produce carboxylic acids and hence are termed as reducing sugars. Aldehydes are more easy to oxidise because they have an open C=O bond. However, ketones can be oxidised as well if they tautomerize to form an aldose first.
5. Hydrolysis
Carbohydrates undergo hydrolysis to produce 𝜶 and 𝜷 isomers. The -OR bond at the anomeric carbon hydrolyses to form a -OH bond.
6. Glycoside Formation
Carbohydrates form glycosides when the anomeric hydroxyl group undergoes condensation with the hydroxyl group of another carbohydrate molecule, eliminating a water molecule.
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