DISACCHARIDES

Carbohydrates which upon hydrolysis give two molecules of the same or different monosaccharides are called disaccharides. Their general formula is C12H22O11. The three most important disaccharides are sucrose, maltose, and lactose. Each one of these on hydrolysis with either an acid or an enzyme gives two molecules of the same  or different monosaccharides as shown below:

2446_disaccharide.JPG

Disaccharides may also be considered to be formed by a condensation reaction between two molecules of the same or different monosaccharides with the eliminatioin of a molecule of water. This reaction involves the formation of an acetal from a hemiacetal and an alcohol – in which one of the monosaccharides acts as the hemiacetal while the other acts as the alcohol.
Sucrose 
It is formed by condensation of one molecule of glucose and one molecule of fructose. Unlike maltose and lactose, it is non-reducing sugar since both glucose (C1 - α) and fructose (C2 -β) are connected to each other through their reducing centres. Its structure is shown below:
Hydrolysis: (Invert Sugar or Invertose). Hydrolysis of sucrose with hot dilute acid yields 
D-glucose and D-fructose.

 2418_disaccharide.JPG

Sucrose is dextrorotatory, its specific rotation being +66.5%, D-glucose is also dextrorotatory, [α]D = +53°, but D-fructose has a large negative rotation, [α]D = -92°. Since D-fructose has a greater specific rotation than D-glucose, the resulting  mixture  is  laevorotatory.   Because   of this the hydrolysis of sucrose is known as the inversion of sucrose, and the equimolecular mixture of glucose and fructose is known is invert sugar or invertose.

 1159_sucrose.JPG

Solved example. The correct haworth projection of sucrose is

 2175_carbo.JPG

Solution:        (B)     Sucrose is composed of α -D- glucose & β - D – fructose.

 2090_carbohydrates.JPG

Solved example.     When sucrose is heated with conc. HNO3 the product is 
            (A)    sucrosenitrate     (B)    oxalic acid 
            (C)    formic acid     (D)    citric acid 
Solution:        (A)

 
Related Resources
Nucleosides and Nucleotides

NUCLEOSIDES AND NUCLEOTIDES Nucleosides:...

Solved Problems on Organic Chemistry

SOLVED PROBLEMS Subjective: Board Types Questions...

Esterification

Esterification Note: HCl first converts the...

Aldotetroses Aldopentoses Aldopentoses and Epimers

Aldotetroses If we examine the general formula of...

Isoelectric Point

ISOELECTRIC POINT (i) When ionized form of amino...

Objective Questions on Carbohydrates Part I

Objective: Prob 1. Peptide linkage is Sol. (D)....

Definition and Classification of Carbohydrates

INTRODUCTION Old Definition The group of compounds...

Cyclic Structure of Monosaccharides

Cyclic structure of Monosaccharides We know that...

Nucleic Acids

NUCLEIC ACIDS Nucleic acids are biologically...

Zwitter Ion

ZWITTER ION (i) Amino acids contain both acidic...

Functions of Nucleic Acids

Biological functions of nucleic acids Important...

Structure of Proteins

Structure of Proteins (i) Proteins have three...

Classification of Carbohydrates

Classification Of Carbohydrates The carbohydrates...

Polysaccharides

POLYSACCHARIDES Polysaccharides are formed when a...

Cyclic Structure of Fructose

Cyclic structure of Fructose Like glucose,...

Cyclic Structure of Anomers

Cyclic Structure of Glucose – Anomers We...

Amino Acids Properties

AMINO ACIDS Introduction (i) Amino acids are...

Essential And Non-Essential Amino Acid

Essential amino acids (a) These must be supplied...

DNA And RNA

DNA And RNA DNA RNA 1. Sugar present in DNA is...

Aldopentoses Aldopentoses and Epimers

Aldopentoses If we examine the general formula of...

Uses of Proteins

Uses of Proteins (i) Protein constitute as...

Mutarotation

MUTAROTATION The two stereoisomeric forms of...

Tests of Proteins

Tests of protein Biuret test (i) On adding a...

Triose

Trioses D and L Terminology: The simplest of all...

Problems on Carbohydrates

MISCELLANEOUS EXERCISES Exercise 1: Explain the...

Monosaccharide

MONOSACCHARIDES The monosaccharides are the basis...

Classification of Amino Acid

Classification Of Amino Acid Amino acid with non...

Synthesis of Alpha Amino Acids

Synthesis of α - amino acids Protein can be...

Classification of Proteins

Classification of Proteins There are two methods...

Peptides And Proteins

PEPTIDES & PROTEINS Introduction (i) Proteins...