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Carbohydrates are a molecule made up of Carbon, Hydrogen and Oxygen only. It is a group that includes sugars, starch and cellulose. They are known as saccharides in terms of biochemistry. There are four types of saccharides based on the number of monomers: monosaccharides, disaccharides, oligosaccharides and polysaccharides.
They are nutritional molecules and are found in a variety of foods. Examples of carbohydrates include glucose, lactose, fructose, sucrose, starch, 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:
Carbohydrates go through SN2 (bimolecular nucleophilic substitution) reaction to produce ethers. They react with alkylating agents such as diazomethane or alkyl iodide and with benzyl halides for benzylation.
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.
It is a nucleophilic addition reaction where the C=O group is reduced to alcohol 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.
Sugars readily undergo oxidation to produce carboxylic acids and hence are termed reducing sugars. Aldehydes are easier to oxidise because they have an open C=O bond. However, ketones can be oxidised only if they tautomerize to form an aldose first.
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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Frequently Asked Questions on Chemical Reactions of Carbohydrates
What are carbohydrates?
Carbohydrates are biomolecules made up of Carbon, Hydrogen and Oxygen only. Structurally a carbohydrate confers to the formula (CH2O)n.
Give some examples of carbohydrates.
Glucose, fructose, galactose, sucrose, maltose, lactose, starch and glycogen are examples of carbohydrates.
What are the chemical reactions that carbohydrates undergo?
Alkylation, Acylation, Reduction, Oxidation, Hydrolysis and Glycoside Formation are the chemical reactions that carbohydrates undergo.
What are reducing sugars?
Sugars can readily undergo oxidation to produce carboxylic acids and hence are termed reducing sugars. Examples include monosaccharides like glucose, fructose, and galactose.