An example of the most common disaccharides in nature (oligosaccharides) is sucrose(beet or cane sugar).

Oligosaccharides are condensation products of two or more monosaccharide molecules.

Disaccharides - these are carbohydrates that, when heated with water in the presence of mineral acids or under the influence of enzymes, undergo hydrolysis, splitting into two molecules of monosaccharides.

Physical properties and occurrence in nature

1. It is colorless crystals with a sweet taste and is highly soluble in water.

2. The melting point of sucrose is 160 °C.

3. When molten sucrose hardens, an amorphous transparent mass is formed - caramel.

4. Contained in many plants: in the sap of birch, maple, carrots, melon, as well as in sugar beets and sugar cane.

Structure and chemical properties

1. The molecular formula of sucrose is C 12 H 22 O 11

2. Sucrose has a more complex structure than glucose. The sucrose molecule consists of glucose and fructose residues connected to each other through the interaction of hemiacetal hydroxyls (1→2)-glycosidic bond:

3. The presence of hydroxyl groups in the sucrose molecule is easily confirmed by reaction with metal hydroxides.

If a solution of sucrose is added to copper (II) hydroxide, a bright blue solution of copper sucrose is formed (a qualitative reaction of polyhydric alcohols).

Video experiment “Proof of the presence of hydroxyl groups in sucrose”

4. There is no aldehyde group in sucrose: when heated with an ammonia solution of silver (I) oxide, it does not give a “silver mirror”; when heated with copper (II) hydroxide, it does not form red copper (I) oxide.

5. Sucrose, unlike glucose, is not an aldehyde. Sucrose, when in solution, does not enter into the “silver mirror” reaction, since it is not able to transform into an open form containing an aldehyde group. Such disaccharides are not capable of oxidation (i.e., being reducing agents) and are called non-restorative sugars.

Video experiment “Lack of reducing ability of sucrose”

6. Sucrose is the most important of the disaccharides.

7. It is obtained from sugar beets (it contains up to 28% sucrose from dry matter) or from sugar cane.

Reaction of sucrose with water.

An important chemical property of sucrose is its ability to undergo hydrolysis (when heated in the presence of hydrogen ions). In this case, from one sucrose molecule a glucose molecule and a fructose molecule are formed:

C 12 H 22 O 11 + H 2 O t , H 2 SO 4 → C 6 H 12 O 6 + C 6 H 12 O 6

Video experiment “Acid hydrolysis of sucrose”

Among the isomers of sucrose with the molecular formula C 12 H 22 O 11, maltose and lactose can be distinguished.

During hydrolysis, various disaccharides are broken down into their constituent monosaccharides by breaking the bonds between them ( glycosidic bonds):

Thus, the hydrolysis reaction of disaccharides is the reverse of the process of their formation from monosaccharides.

Application of sucrose

· Food product;

· In the confectionery industry;

· Obtaining artificial honey

1. It is colorless crystals with a sweet taste and is highly soluble in water.

2. The melting point of sucrose is 160 °C.

3. When molten sucrose hardens, an amorphous transparent mass is formed - caramel.

4. Contained in many plants: in the sap of birch, maple, carrots, melon, as well as in sugar beets and sugar cane.

Structure and chemical properties.

1. The molecular formula of sucrose is C 12 H 22 O 11.

2. Sucrose has a more complex structure than glucose.

3. The presence of hydroxyl groups in the sucrose molecule is easily confirmed by reaction with metal hydroxides.

If a solution of sucrose is added to copper(II) hydroxide, a bright blue solution of copper sucrose is formed.

4. There is no aldehyde group in sucrose: when heated with an ammonia solution of silver (I) oxide, it does not give a “silver mirror”; when heated with copper (II) hydroxide, it does not form red copper (I) oxide.

5. Sucrose, unlike glucose, is not an aldehyde.

6. Sucrose is the most important of the disaccharides.

7. It is obtained from sugar beets (it contains up to 28% sucrose from dry matter) or from sugar cane.

Reaction of sucrose with water.

If you boil a solution of sucrose with a few drops of hydrochloric or sulfuric acid and neutralize the acid with alkali, and then heat the solution with copper (II) hydroxide, a red precipitate forms.

When a sucrose solution is boiled, molecules with aldehyde groups appear, which reduce copper (II) hydroxide to copper (I) oxide. This reaction shows that sucrose, under the catalytic action of an acid, undergoes hydrolysis, resulting in the formation of glucose and fructose:

C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6.

6. The sucrose molecule consists of glucose and fructose residues connected to each other.

Among the isomers of sucrose with the molecular formula C 12 H 22 O 11, maltose and lactose can be distinguished.

Features of maltose:

1) maltose is obtained from starch under the action of malt;

2) it is also called malt sugar;

3) upon hydrolysis it forms glucose:

C 12 H 22 O 11 (maltose) + H 2 O → 2 C 6 H 12 O 6 (glucose).

Features of lactose: 1) lactose (milk sugar) is found in milk; 2) it is highly nutritious; 3) during hydrolysis, lactose decomposes into glucose and galactose - an isomer of glucose and fructose, which is an important feature.

66. Starch and its structure

Physical properties and occurrence in nature.

1. Starch is a white powder that is insoluble in water.

2. In hot water it swells and forms a colloidal solution - a paste.

3. Being a product of the absorption of carbon monoxide (IV) by green (chlorophyll-containing) plant cells, starch is widespread in the plant world.

4. Potato tubers contain about 20% starch, wheat and corn grains - about 70%, rice - about 80%.

5. Starch is one of the most important nutrients for humans.

The structure of starch.

1. Starch (C 6 H 10 O 5) n is a natural polymer.

2. It is formed as a result of the photosynthetic activity of plants when absorbing the energy of solar radiation.

3. First, glucose is synthesized from carbon dioxide and water as a result of a series of processes, which general view can be expressed by the equation: 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2.

5. Macromolecules of starch are not the same in size: a) they contain different number C 6 H 10 O 5 units - from several hundred to several thousand, while their molecular weight is also different; b) they also differ in structure: along with linear molecules with a molecular weight of several hundred thousand, there are molecules of a branched structure, the molecular weight of which reaches several millions.

Chemical properties of starch.

1. One of the properties of starch is the ability to give a blue color when interacting with iodine. This coloring is easy to observe if you place a drop of iodine solution on a cut of potato or a slice of white bread and heat the starch paste with copper (II) hydroxide, the formation of copper (I) oxide will be visible.

2. If you boil a starch paste with a small amount of sulfuric acid, neutralize the solution and react with copper (II) hydroxide, a characteristic precipitate of copper (I) oxide is formed. That is, when heated with water in the presence of an acid, starch undergoes hydrolysis, resulting in the formation of a substance that reduces copper (II) hydroxide into copper (I) oxide.

3. The process of splitting starch macromolecules with water occurs gradually. First, intermediate products with a lower molecular weight than starch are formed - dextrins, then an isomer of sucrose - maltose, the final product of hydrolysis is glucose.

4. The reaction of converting starch into glucose under the catalytic action of sulfuric acid was discovered in 1811 by a Russian scientist K. Kirchhoff. The method he developed for producing glucose is still used today.

5. Starch macromolecules consist of residues of cyclic L-glucose molecules.

Exists different types Sahara. The simplest type is monosaccharides, which include and galactose. Table or granulated sugar commonly used in food is a disaccharide. Other disaccharides are maltose and lactose.

Types of sugar involving long chains of molecules are called oligosaccharides.

Most compounds of this type are expressed using the formula CnH2nOn. (n is a number that can range from 3 to 7). The formula of glucose is C6H12O6.

Some monosaccharides can form bonds with other monosaccharides to form disaccharides (sucrose) and polysaccharides (starch). When sugar is eaten, enzymes break down these bonds and it is digested. After digestion and absorption into the blood and tissues, monosaccharides are converted into, and galactose.

The monosaccharides pentose and hexose form a ring structure.

Basic monosaccharides

The main monosaccharides include glucose, fructose and galactose. They have five hydroxyl groups (-OH) and one carbonyl group (C=0).

Glucose, dextrose or grape sugar is found in fruits and vegetable juices. It is the primary product of photosynthesis. Glucose can be produced by the addition of enzymes or in the presence of acids.

Fructose or fruit sugar is present in fruits, some root vegetables, cane honey and honey. This is the most sweet sugar. Fructose is part of table sugar or.

Galactose is not found in pure form. But it is part of the glucose disaccharide lactose or milk sugar. It is less sweet than glucose. Galactose is part of the antigens found on the surface of blood vessels.

Disaccharides

Sucrose, maltose and lactose are disaccharides.

Chemical disaccharide - C12H22O11. They are formed by combining two monosaccharide molecules with the exception of one water molecule.

Sucrose occurs naturally in the stems of cane sugar and the roots of sugar beets, some plants, and carrots. The sucrose molecule is a combination of fructose and glucose molecules. Its molar mass is 342.3.

Maltose is formed during the germination of seeds of some plants, such as barley. The maltose molecule is formed by combining two glucose molecules. This sugar is less sweet than glucose, sucrose and fructose.

Lactose is found in milk. Its molecule is a combination of galactose and glucose molecules.

How to find the molar mass of a sugar molecule

Molar mass of C12H22O11 = 12 (mass C) + 22 (mass H) + 11 (mass O) = 12 (12.01) + 22 (1.008) + 11 (16) = 342.30

It is useful to know the chemical formulas of substances common in everyday life not only as part of a school chemistry course, but also simply for general erudition. Almost everyone knows the formula for water or table salt, but few can immediately get to the point about alcohol, sugar or vinegar. Let's go from simple to complex.

What is the formula of water?

This liquid, thanks to which an amazing wildlife, everyone knows and drinks. Moreover, it makes up about 70% of our body. Water is the simplest compound of an oxygen atom with two hydrogen atoms.

Chemical formula of water: H 2 O

What is the formula for table salt?

Table salt is not only an indispensable culinary dish, but also one of the main components of sea salt, the reserves of which in the World Ocean amount to millions of tons. The formula for table salt is simple and easy to remember: 1 sodium atom and 1 chlorine atom.

Chemical formula of table salt: NaCl

What is the formula for sugar?

Sugar is a white crystalline powder, without which not a single sweet tooth in the world can live a day. Sugar is complex organic compound, the formula of which you won’t immediately remember: 12 carbon atoms, 22 hydrogen atoms and 11 oxygen atoms form a sweet and complex structure.

Chemical formula of sugar: C 12 H 22 O 11

What is the formula for vinegar?

Vinegar is a solution of acetic acid that is used for food and also for cleaning metals from plaque. The acetic acid molecule has a complex structure, consisting of two carbon atoms, to one of which three hydrogen atoms are attached, and to the other two oxygen atoms, one of which has grabbed another hydrogen.

Chemical formula of acetic acid: CH 3 COOH

What is the formula of alcohol?

Let's start with the fact that there are different types of alcohols. The alcohol that is used to make wine, vodka and cognac is scientifically called ethanol. In addition to ethanol, there are also a bunch of alcohols that are used in medicine, automotive and aviation.

Chemical formula of ethanol: C 2 H 5 OH

What is the formula for baking soda?

Baking soda is scientifically called sodium bicarbonate. From this name, any novice chemist will understand that the soda molecule contains sodium, carbon, oxygen and hydrogen.

Chemical formula baking soda: NaHCO3

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Chemical properties sucrose

In sucrose solution, ring opening does not occur, so it does not have the properties of aldehydes.

1) Hydrolysis (in acidic environment):

C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6.

sucrose glucose fructose

2) Being a polyhydric alcohol, sucrose gives a blue color to the solution when reacting with Cu(OH) 2.

3) Interaction with calcium hydroxide to form calcium sucrose.

4) Sucrose does not react with an ammonia solution of silver oxide, so it is called a non-reducing disaccharide.

Polysaccharides.

Polysaccharides– high molecular weight non-sugar-like carbohydrates containing from ten to hundreds of thousands of monosaccharide residues (usually hexoses) linked by glycosidic bonds.

The most important polysaccharides are starch and cellulose (fiber). They are built from glucose residues. The general formula of these polysaccharides is (C 6 H 10 O 5) n. In the formation of polysaccharide molecules, glycosidic (at the C 1 atom) and alcoholic (at the C 4 atom) hydroxyls usually take part, i.e. a (1–4)-glycosidic bond is formed.

From the point of view general principles structurally, polysaccharides can be divided into two groups, namely: homopolysaccharides, consisting of monosaccharide units of only one type, and heteropolysaccharides, which are characterized by the presence of two or more types of monomer units.

From a functional point of view, polysaccharides can also be divided into two groups: structural and reserve polysaccharides. Important structural polysaccharides are cellulose and chitin (in plants and animals, as well as in fungi, respectively), and the main reserve polysaccharides are glycogen and starch (in animals, as well as in fungi, and plants, respectively). Only homopolysaccharides will be considered here.

Cellulose (fiber)− the most widespread structural polysaccharide of the plant world.

Main component plant cell, synthesized in plants (wood contains up to 60% cellulose). Cellulose has great mechanical strength and acts as a support material for plants. Wood contains 50-70% cellulose, cotton is almost pure cellulose.

Pure cellulose is a white fibrous substance, tasteless and odorless, insoluble in water and other solvents.

Cellulose molecules have a linear structure and high molecular weight; they consist only of unbranched molecules in the form of threads, because the shape of β-glucose residues excludes helicalization. Cellulose consists of thread-like molecules, which are assembled into bundles by hydrogen bonds of hydroxyl groups within the chain, as well as between adjacent chains. It is this packaging of chains that provides high mechanical strength, fibrousness, insolubility in water and chemical inertness, which makes cellulose ideal material to build cell walls.

Cellulose consists of α,D-glucopyranose residues in their β-pyranose form, i.e., in the cellulose molecule, β-glucopyranose monomer units are linearly connected to each other by β-1,4-glucosidic bonds:

With partial hydrolysis of cellulose, the disaccharide cellobiose is formed, and with complete hydrolysis, D-glucose is formed. Molecular weight cellulose 1,000,000−2,000,000. Fiber is not digested by enzymes gastrointestinal tract, since the set of these enzymes of the human gastrointestinal tract does not contain β-glucosidase. However, it is known that the presence of optimal amounts of fiber in food promotes the formation of feces. With the complete exclusion of fiber from food, the formation of feces is disrupted.

Starch- a polymer of the same composition as cellulose, but with an elementary unit representing an α-glucose residue:

Starch molecules are coiled, most of the molecules are branched. The molecular weight of starch is less than the molecular weight of cellulose.

Starch is an amorphous substance, a white powder consisting of small grains, insoluble in cold water, but partially soluble in hot.

Starch is a mixture of two homopolysaccharides: linear - amylose and branched - amylopectin, the general formula of which is (C 6 H 10 O 5) n.

When starch is treated with warm water, it is possible to isolate two fractions: a fraction soluble in warm water and consisting of amylose polysaccharide, and a fraction that only swells in warm water to form a paste and consists of amylopectin polysaccharide.

Amylose has a linear structure, α, D-glucopyranose residues are linked by (1–4)-glycosidic bonds. The unit cell of amylose (and starch in general) is represented as follows:

The amylopectin molecule is built in a similar way, but has branches in the chain, which creates a spatial structure. At branching points, monosaccharide residues are linked by (1–6)-glycosidic bonds. Between the branch points there are usually 20-25 glucose residues.

(amylopectin)

As a rule, the amylose content in starch is 10-30%, amylopectin - 70-90%. Starch polysaccharides are built from glucose residues connected in amylose and in the linear chains of amylopectin by α-1,4-glucosidic bonds, and at the branch points of amylopectin by interchain α-1,6-glucosidic bonds.

An amylose molecule contains, on average, about 1000 glucose residues; individual linear sections of the amylopectin molecule consist of 20-30 such units.

In water, amylose does not give a true solution. The amylose chain in water forms hydrated micelles. In solution, when iodine is added, amylose becomes colored blue. Amylopectin also produces micellar solutions, but the shape of the micelles is slightly different. The polysaccharide amylopectin is stained red-violet with iodine.

Starch has a molecular weight of 10 6 -10 7. With partial acid hydrolysis of starch, polysaccharides of a lower degree of polymerization are formed - dextrins, with complete hydrolysis - glucose. Starch is the most important dietary carbohydrate for humans. Starch is formed in plants during photosynthesis and is deposited as a “reserve” carbohydrate in roots, tubers and seeds. For example, grains of rice, wheat, rye and other cereals contain 60-80% starch, potato tubers - 15-20%. A related role in the animal world is played by the polysaccharide glycogen, which is “stored” mainly in the liver.

Glycogen− the main reserve polysaccharide of higher animals and humans, built from α-D-glucose residues. The empirical formula of glycogen, like starch, is (C 6 H 10 O 5) n. Glycogen is found in almost all organs and tissues of animals and humans; the largest amount is found in the liver and muscles. The molecular weight of glycogen is 10 7 -10 9 and higher. Its molecule is built from branching polyglucosidic chains, in which glucose residues are connected by α-1,4-glucosidic bonds. There are α-1,6-glucosidic bonds at the branch points. Glycogen is close in structure to amylopectin.

In the glycogen molecule, there are internal branches - sections of polyglucoside chains between branch points, and external branches - sections from the peripheral branch point to the non-reducing end of the chain. During hydrolysis, glycogen, like starch, is broken down to form first dextrins, then maltose and, finally, glucose.

Chitin− structural polysaccharide of lower plants, especially fungi, as well as invertebrate animals (mainly arthropods). Chitin consists of 2-acetamido-2-deoxy-D-glucose residues linked by β-1,4-glucosidic bonds.