Notes On Carbohydrates: Classification - CBSE Class 12 Chemistry
Carbohydrates are a vital source of the three basic necessities of life, that is, food, clothing and shelter. Carbohydrates constitute a very large group among various naturally occurring organic compounds. In nature, they are primarily produced by plants during photosynthesis.
EX: Cane sugar, Glucose and starch.

Carbohydrates are considered to be Hydrates of carbon. These are also called saccharides. Carbohydrates have the general formula Cx(H2O)y.
EX: Glucose, C6H12O6: Its formula can be rearranged to C6(H2O)6.

Classification of carbohydrates:
 
Carbohydrates can be classified based on their behaviour during hydrolysis—these include monosaccharides, oligosaccharides and polysaccharides.
 
Mono-saccharides:

These are the basic building blocks of all carbohydrates. About 20 monosaccharides exist in nature.
EX: Glucose, fructose, arabinose and ribose.

 

Oligosaccharides:
 
The Carbohydrates which yield 2 - 10 monosaccharide units when hydrolysed are called ‘oligosaccharides’, these can be further classified into disaccharides, tri-saccharides, tetra-
Saccharides.
 
 
On hydrolysis, a molecule of a disaccharide yields two molecules of monosaccharides.
EX: Sucrose, lactose and maltose.  

Sucrose molecule on hydrolysis produces glucose &fructose molecules.
 

 
Polysaccharides yield a large number of monosaccharide units when hydrolysed.
EX: starch, cellulose, glycogen and many gums, do not have a sweet taste. Hence, they are referred to as “non-sugars”.

In general, monosaccharides and oligosaccharides are sweet in taste, and are, called as “sugars’.
EX: sucrose, found in cane sugar, and lactose, found in milk.

Carbohydrates can also be classified as “reducing sugars” and non-reducing sugars.  Reducing sugars are carbohydrates that reduce Fehling’s solution or Tollen’s reagent.
EX: Monosaccharides

Non-reducing sugars are carbohydrates that can’t reduce Fehling’s solution (or) Tollen’s reagent.
EX: Polysaccharides

Most disaccharides are reducing sugars but sucrose can’t reduce Fehling’s solution (or) Tollen’s reagent.

Monosaccharides can be further classified into two major categories on the basis of the nature of the carbonyl group present, as aldoses and ketoses.

Aldoses and ketoses can be further classified on the basis of the number of carbon atoms present.
EX: Trioses, Pentoses...etc.

Summary

Carbohydrates are a vital source of the three basic necessities of life, that is, food, clothing and shelter. Carbohydrates constitute a very large group among various naturally occurring organic compounds. In nature, they are primarily produced by plants during photosynthesis.
EX: Cane sugar, Glucose and starch.

Carbohydrates are considered to be Hydrates of carbon. These are also called saccharides. Carbohydrates have the general formula Cx(H2O)y.
EX: Glucose, C6H12O6: Its formula can be rearranged to C6(H2O)6.

Classification of carbohydrates:
 
Carbohydrates can be classified based on their behaviour during hydrolysis—these include monosaccharides, oligosaccharides and polysaccharides.
 
Mono-saccharides:

These are the basic building blocks of all carbohydrates. About 20 monosaccharides exist in nature.
EX: Glucose, fructose, arabinose and ribose.

 

Oligosaccharides:
 
The Carbohydrates which yield 2 - 10 monosaccharide units when hydrolysed are called ‘oligosaccharides’, these can be further classified into disaccharides, tri-saccharides, tetra-
Saccharides.
 
 
On hydrolysis, a molecule of a disaccharide yields two molecules of monosaccharides.
EX: Sucrose, lactose and maltose.  

Sucrose molecule on hydrolysis produces glucose &fructose molecules.
 

 
Polysaccharides yield a large number of monosaccharide units when hydrolysed.
EX: starch, cellulose, glycogen and many gums, do not have a sweet taste. Hence, they are referred to as “non-sugars”.

In general, monosaccharides and oligosaccharides are sweet in taste, and are, called as “sugars’.
EX: sucrose, found in cane sugar, and lactose, found in milk.

Carbohydrates can also be classified as “reducing sugars” and non-reducing sugars.  Reducing sugars are carbohydrates that reduce Fehling’s solution or Tollen’s reagent.
EX: Monosaccharides

Non-reducing sugars are carbohydrates that can’t reduce Fehling’s solution (or) Tollen’s reagent.
EX: Polysaccharides

Most disaccharides are reducing sugars but sucrose can’t reduce Fehling’s solution (or) Tollen’s reagent.

Monosaccharides can be further classified into two major categories on the basis of the nature of the carbonyl group present, as aldoses and ketoses.

Aldoses and ketoses can be further classified on the basis of the number of carbon atoms present.
EX: Trioses, Pentoses...etc.

Videos

References

Previous
Next