Which molecules have a double bond? Double bond

Chemical bond

All interactions leading to the combination of chemical particles (atoms, molecules, ions, etc.) into substances are divided into chemical bonds and intermolecular bonds (intermolecular interactions).

Chemical bonds- bonds directly between atoms. There are ionic, covalent and metallic bonds.

Intermolecular bonds- connections between molecules. These are hydrogen bonds, ion-dipole bonds (due to the formation of this bond, for example, the formation of a hydration shell of ions occurs), dipole-dipole (due to the formation of this bond, molecules of polar substances are combined, for example, in liquid acetone), etc.

Ionic bond - chemical bond, formed due to the electrostatic attraction of oppositely charged ions. In binary compounds (compounds of two elements), it is formed when the sizes of the bonded atoms differ greatly from each other: some atoms are large, others are small - that is, some atoms easily give up electrons, while others tend to accept them (usually these are atoms of the elements that form typical metals and atoms of elements forming typical nonmetals); the electronegativity of such atoms is also very different.
Ionic bonding is non-directional and non-saturable.

Covalent bond- a chemical bond that occurs due to the formation of a common pair of electrons. A covalent bond is formed between small atoms with the same or similar radii. Prerequisite- the presence of unpaired electrons in both bonded atoms (exchange mechanism) or a lone pair in one atom and a free orbital in the other (donor-acceptor mechanism):

According to the number of common electron pairs covalent bonds are divided into
• simple (single)- one pair of electrons,
• double- two pairs of electrons,
• triples- three pairs of electrons.

Double and triple bonds are called multiple bonds.

According to the distribution of electron density between the bonded atoms, a covalent bond is divided into non-polar And polar. Not polar connection is formed between identical atoms, polar - between different ones.

Electronegativity- a measure of the ability of an atom in a substance to attract common electron pairs.
The electron pairs of polar bonds are shifted towards more electronegative elements. The displacement of electron pairs itself is called bond polarization. The partial (excess) charges formed during polarization are designated + and -, for example: .

Based on the nature of the overlap of electron clouds ("orbitals"), a covalent bond is divided into -bond and -bond.
-A bond is formed due to the direct overlap of electron clouds (along the straight line connecting the atomic nuclei), -a bond is formed due to lateral overlap (on both sides of the plane in which the atomic nuclei lie).

A covalent bond is directional and saturable, as well as polarizable.
To explain and predict the mutual direction of valence bonds use the hybridization model.

Hybridization atomic orbitals and electronic clouds- the supposed alignment of atomic orbitals in energy, and electron clouds in shape when an atom forms covalent bonds.
The three most common types of hybridization are: sp-, sp 2 and sp 3 -hybridization. For example:
sp-hybridization - in molecules C 2 H 2, BeH 2, CO 2 (linear structure);
sp 2-hybridization - in molecules C 2 H 4, C 6 H 6, BF 3 (flat triangular shape);
sp 3-hybridization - in molecules CCl 4, SiH 4, CH 4 (tetrahedral form); NH 3 (pyramidal shape); H 2 O (angular shape).

Metal connection- chemical bond formed due to socialization valence electrons of all bonded atoms of a metal crystal. As a result, a single electron cloud of the crystal is formed, which easily moves under the influence of electrical voltage- from here high electrical conductivity metals
A metallic bond is formed when the atoms being bonded are large and therefore tend to give up electrons. Simple substances with a metallic bond are metals (Na, Ba, Al, Cu, Au, etc.), complex substances are intermetallic compounds (AlCr 2, Ca 2 Cu, Cu 5 Zn 8, etc.).
The metal bond does not have directionality or saturation. It is also preserved in metal melts.

Hydrogen bond- an intermolecular bond formed due to the partial acceptance of a pair of electrons from a highly electronegative atom by a hydrogen atom with a large positive partial charge. It is formed in cases where one molecule contains an atom with a lone pair of electrons and high electronegativity (F, O, N), and the other contains a hydrogen atom bound by a highly polar bond to one of such atoms. Examples of intermolecular hydrogen bonds:

H—O—H OH 2 , H—O—H NH 3 , H—O—H F—H, H—F H—F.

Intramolecular hydrogen bonds exist in the molecules of polypeptides, nucleic acids, proteins, etc.

A measure of the strength of any bond is the bond energy.
Communication energy- the energy required to break a given chemical bond in 1 mole of a substance. The unit of measurement is 1 kJ/mol.

The energies of ionic and covalent bonds are of the same order of magnitude, the energy of hydrogen bonds is an order of magnitude lower.

The energy of a covalent bond depends on the size of the bonded atoms (bond length) and on the multiplicity of the bond. The smaller the atoms and the greater the bond multiplicity, the greater its energy.

The ionic bond energy depends on the size of the ions and their charges. The smaller the ions and the greater their charge, the greater the binding energy.

Structure of matter

According to the type of structure, all substances are divided into molecular And non-molecular. Among organic matter molecular substances predominate; among inorganic substances, non-molecular substances predominate.

Based on the type of chemical bond, substances are divided into substances with covalent bonds, substances with ionic bonds (ionic substances) and substances with metallic bonds (metals).

Substances with covalent bonds can be molecular or non-molecular. This significantly affects their physical properties.

Molecular substances consist of molecules connected to each other by weak intermolecular bonds, these include: H 2, O 2, N 2, Cl 2, Br 2, S 8, P 4 and others simple substances; CO 2, SO 2, N 2 O 5, H 2 O, HCl, HF, NH 3, CH 4, C 2 H 5 OH, organic polymers and many other substances. These substances do not have high strength, they have low temperatures melting and boiling, do not carry out electric current, some of them are soluble in water or other solvents.

Non-molecular substances with covalent bonds or atomic substances(diamond, graphite, Si, SiO 2, SiC and others) form very strong crystals (with the exception of layered graphite), they are insoluble in water and other solvents, have high temperatures melting and boiling, most of them do not conduct electric current (except for graphite, which is electrically conductive, and semiconductors - silicon, germanium, etc.)

All ionic substances are naturally non-molecular. These are solid, refractory substances, solutions and melts of which conduct electric current. Many of them are soluble in water. It should be noted that in ionic substances ah, the crystals of which consist of complex ions, there are also covalent bonds, for example: (Na +) 2 (SO 4 2-), (K +) 3 (PO 4 3-), (NH 4 +)(NO 3-) etc. The atoms that make up complex ions are connected by covalent bonds.

Metals (substances with metallic bonds) very diverse in their physical properties. Among them there are liquid (Hg), very soft (Na, K) and very hard metals (W, Nb).

Characteristic physical properties metals are their high electrical conductivity (unlike semiconductors, it decreases with increasing temperature), high heat capacity and ductility (for pure metals).

In the solid state, almost all substances are composed of crystals. According to the type of structure and type of chemical bond, crystals (" crystal lattices") divided by atomic(crystals are not molecular substances with a covalent bond), ionic(crystals of ionic substances), molecular(crystals of molecular substances with covalent bonds) and metal(crystals of substances with a metallic bond).

Tasks and tests on the topic "Topic 10. "Chemical bonding. Structure of matter."

• Types of chemical bond - Structure of matter grade 8–9

  Lessons: 2 Assignments: 9 Tests: 1

• Assignments: 9 Tests: 1

After working on this topic, you should understand the following concepts: chemical bonding, intermolecular bonding, ionic bond, covalent bond, metal bond, hydrogen bond, simple connection, double bond, triple bond, multiple bonds, non-polar bond, polar bond, electronegativity, bond polarization, - and - bond, hybridization of atomic orbitals, bond energy.

You must know the classification of substances by type of structure, by type of chemical bond, the dependence of the properties of simple and complex substances on the type of chemical bond and the type of “crystal lattice”.

You must be able to: determine the type of chemical bond in a substance, the type of hybridization, draw up diagrams of bond formation, use the concept of electronegativity, a number of electronegativity; know how electronegativity changes chemical elements one period, and one group to determine the polarity of a covalent bond.

After making sure that everything you need has been learned, proceed to completing the tasks. We wish you success.

• O. S. Gabrielyan, G. G. Lysova. Chemistry 11th grade. M., Bustard, 2002.
• G. E. Rudzitis, F. G. Feldman. Chemistry 11th grade. M., Education, 2001.

Double bond

a covalent four-electron bond between two adjacent atoms in a molecule. D. s. usually indicated by two valence primes: >C=C<, >C=N ≈, >C=O, >C=S, ≈ N=N ≈, ≈ H=O, etc. This implies that one pair of electrons with sp2 or sp hybridized orbitals forms an s-bond (see. rice. 1), the electron density of which is concentrated along the interatomic axis; An s-bond is similar to a simple bond. Another pair of electrons with p-orbitals forms a p-bond, the electron density of which is concentrated outside the interatomic axis. If in education D. s. atoms of group IV or V participate periodic table, then these atoms and the atoms directly connected to them are located in the same plane; bond angles are equal to 120╟. In the case of asymmetrical systems, distortion is possible molecular structure. D. s. shorter than a simple bond and characterized by a high energy barrier to internal rotation; Therefore, the positions of the substituents on atoms bonded to the bond are not equivalent, and this causes the phenomenon of geometric isomerism. Compounds containing D. are capable of addition reactions. If D. s. is electronically symmetric, then the reactions are carried out both by radical (by homolysis of the p-bond) and by ionic mechanisms (due to the polarizing effect of the medium). If the electronegativities of the atoms bonded to the bond are different or if different substituents are bonded to them, then the p-bond is highly polarized. Compounds containing polar D. are prone to addition by an ionic mechanism: to electron-withdrawing D. with. Nucleophilic reagents easily attach, and electron-donating reagents. ≈ electrophilic. The direction of electron displacement during D. polarization. It is customary to indicate with arrows in formulas, and the resulting excess charges with symbols d- And d+. This makes it easier to understand the radical and ion mechanisms addition reactions:

In compounds with two dynamic bonds separated by one simple bond, p-bonds are conjugated and a single p-electron cloud is formed, the lability of which is manifested along the entire chain ( rice. 2, left). The consequence of this conjugation is the ability to undergo 1,4-addition reactions:

If three D. s. are conjugated in a six-membered ring, then the sextet of p-electrons becomes common to the entire cycle and a relatively stable aromatic system is formed (see. rice. 2, right). The addition of both electrophilic and nucleophilic reagents to such compounds is energetically hindered. (See also Chemical bond.)

G. A. Sokolsky.

Wikipedia

Double bond (disambiguation)

Double bond:

• A double bond is a chemical bond between two atoms formed by two pairs of electrons; special case multiple connection.
• Double bind - the same as double message, a psychological concept in Gregory Bateson's theory of schizophrenia.

Double bond

Double bond- a covalent bond between two atoms in a molecule through two shared electron pairs. The structure of a double bond is reflected in the theory of valence bonds. In this theory, it was believed that a double bond is formed by a combination of sigma (Fig. 1) and pi (Fig. 2) bonds.

At a symposium on theoretical organic chemistry(London, September 1958) a report was presented by L. Pauling, twice laureate Nobel Prizes. Pauling's report was devoted to the nature of the double bond. Was suggested new way descriptions of a double bond as a combination of two identical bent bonds.

Describing double and triple bonds using the concept of curved bonds explains some of their properties in a striking way. So, if multiple bonds have the form of arcs with a length of 1.54 Å (the length of a single carbon-carbon bond) and starting direction coincides with the tetrahedral one, then their calculated length turns out to be equal to 1.32 Å for a double bond and 1.18 Å for a triple bond, which corresponds well experimental values 1.33 and 1.20 Å."

Further development ideas about the electrostatic repulsion of electrons were undertaken in the theory of repulsion of electron pairs by R. Gillespie.

Ethylene for organic chemistry is, perhaps, not a brick, but a whole block. The ethylene molecule consists of two carbon atoms and four hydrogen atoms.
How is ethylene built? Indeed, in all organic compounds carbon must be tetravalent, and in the ethylene molecule each carbon atom is bonded to another carbon and two hydrogens, i.e., as if trivalent.
No, no violation of the principle of tetravalency of carbon is observed in the ethylene molecule: two carbon atoms are connected to each other not by a simple one, as in ethane, but by a double bond. Each valency is indicated by a line, and if we connect two carbon atoms with two lines, we keep the carbon tetravalent:
But what is hidden behind such designations, how does the connection depicted by one line differ from the connection depicted by two lines?
Let's remember how the ethane molecule is formed. Around each carbon atom, as a result of hybridization, i.e. mixing, averaging of one 5- and three p-orbitals, four directed in different sides absolutely identical hybridized 5p3 orbitals.

In the case of ethylene, the bonds between carbon atoms are constructed differently. Here, only two orbitals mix with one 5 orbital. As a result, three hybridized 5p2 orbitals are formed, which lie in the same plane: two of them overlap with the 5 orbitals of two hydrogen atoms and bind these hydrogens to carbon, and the third $p2 orbital overlaps with exactly the same orbital of the second carbon atom. This bond accounts for one of the lines between two carbon atoms. What does the second line symbolize?
Let's remember: we still have one more p-electron. It forms a cloud in the form of a volumetric figure eight, which is directed perpendicular to the plane of three orbitals. These electron clouds (one figure eight from each carbon) can also overlap with each other, but not “head to head”, as two $p2 orbitals overlap, but "sideways". This overlap is indicated by the second dash. The connection of the first type (“foreheads”) is designated Greek letter a (sigma), and the bond in which the electron clouds overlap “sides” is called an i-bond (and such electrons themselves are called i-electrons). All together this is a double bond. The double bond is shorter than the single bond, its length is 0.133 mm.
So, we have disassembled the structure of another part from which we can build “buildings” organic compounds. What kind of buildings are these?
Let us first take the following combinations: one ethylene molecule and several methane molecules. If one hydrogen atom in an ethylene molecule is replaced by a methyl group (i.e., a methane residue), we obtain propylene (otherwise called propene) CH2=CH-CH3.
Now let's construct the next term homologous series(i.e. the member with one more CH2 group). To do this, we replace one of the hydrogen atoms in propylene with a methyl group. There are several possibilities for such substitution; as a result, we get three different butylenes (butenes).
Replacing the hydrogen of the methyl group, we arrive at normal butene-1: CH2=CH—CH2—CH3. Substituting hydrogen at the other end will give butene-2: CH3—€H=CH—CH3. Finally, replacing the only hydrogen at the double bond, we get mso-butylene: CH2=C(CH3)2. These are three different substances that have different temperatures boiling and melting. The composition of all these hydrocarbons is reflected general formula XiaN2p. Similarly, you can derive the formulas of all possible pentenes, hexenes, etc.
So we have learned to receive Not saturated hydrocarbons on paper. How do you actually get them?
The main source of the simplest alkenes (i.e., unsaturated hydrocarbons) are petroleum products, from which ethylene is isolated after heating and distillation.
propylene, butylenes... If you heat an alkane (saturated hydrocarbon) to 500-600 °C under high pressure in the presence of a catalyst, then two hydrogen atoms are split off and an alkene is formed. From n-butane, for example, a mixture of butene-1 and butene-2 ​​is obtained.
In the laboratory, unsaturated hydrocarbons (for example, ethylene) are obtained by removing water from alcohols; To do this, they are heated with a catalytic amount of acid:
IDO 200 °C CH3—CH2—OH ----- CH2=CH2
It is also possible to split off a hydrogen halide molecule with an alkali from halogen derivatives of saturated hydrocarbons:
NaON
СНз-СНз-СН2С1 Ш СНз-СН=СН2-НС!
The range of reactions into which compounds with a double bond enter is much more diverse and wider than the set of transformations of alkanes. Let's consider one of these reactions of unsaturated compounds.
Unsaturated substances add halogen-hydrogens at the double bond, and halogen-substituted saturated hydrocarbons are formed (i.e., the opposite reaction to the one just written occurs). But if you add a hydrogen halide to an unsymmetrical alkene. (to one in which both sides of the double bond are located various groups), then two different derivatives can be obtained, for example, in the case of propene, either CH3CHHCH2C1 or CH3CHNH3.
This reaction was studied by the Russian chemist V.V. Markovnikov back in the last century. He established the rule that now bears his name: a halogen attaches to the least hydrogenated carbon atom (i.e., the one bonded to the smallest number hydrogen atoms). This means that mainly isopropyl chloride CH3CHC1CH3 is formed from propylene. But why reaction is underway exactly like that? Modern theory gives an explanation of Markovikov's rule. We will present this theory in a somewhat simplified form.
The fact is that mechanisms even simple at first glance chemical reactions quite complex, including several stages. So it is with the addition reaction of hydrogen halide. A hydrogen chloride molecule does not attach to an alkene molecule immediately, but in parts. Hydrogen is added first in the form of the P1+ proton. A positively charged proton approaches a propylene molecule. Which carbon atom connected by a double bond will it attack? It turns out that it is the outermost one, because it contains a small negative charge, designated b— (delta minus). But how did this charge, this slight excess of electron density, arise?
The methyl group is to blame for this. It seems to push electrons away from itself, which therefore accumulate at the opposite carbon atom, away from the methyl group. Let us just emphasize once again that this shift in electron density is very small. It is much less than if a whole electron moved from the middle carbon atom to the outer one. Then we would have to put a plus over the middle atom, and a minus over the extreme one (we put the sign d—, which means a small part of the total negative charge electron).
So, it is now clear that a positively charged proton will much more readily approach the outermost carbon atom, which carries some excess electron density.
A positively charged proton attaches to an uncharged molecule and transfers its charge to it. Where will this charge be located? If a proton were to attach to the middle carbon atom, a charge would appear on the outermost carbon. In fact, the proton approaches the outermost carbon atom, and the charge arises on the middle carbon. Does it make a difference where the charge is concentrated? Yes, and there is a big difference. Both carbocations (i.e. organic particles, carrying positive charge on a carbon atom) are unstable and live very short. But still, the second cation is more stable: the fact is that it is surrounded on both sides by methyl groups; and we already know that methyl groups are capable of donating electrons and repelling them. It turns out that the methyl groups partially compensate for the resulting positive charge. And the smaller this charge, the more stable the carbocation. In the first case, the positive charge is extinguished by only one ethyl group; this carbocation will be less stable than the second.
As a rule, the more stable a particle is, the easier it is to form. This means that the second carbocation will be obtained much more often than the first. The second stage of the reaction is the addition of a negatively charged chlorine ion to the carbocation. Since the carbocation of the second type predominates in the products of the first stage, as a result of the entire reaction, one molecule of 1-chloropropane produces thousands of molecules of the isomer in which chlorine is attached to the middle carbon. That is why we say that the accession proceeds mainly according to the Markovnikov rule. Two factors—the location of the proton attack in the first stage and the stability of the carbocation formed after this—determine the fulfillment of this rule.
Unsaturated compounds are easily attached not only hydrogen chloride, but also. many other molecules. Typical examples chemical transformations ethylene are shown in the diagram.
The reader may wonder: are there any organic molecules, built only from ethylene blocks? Yes, they do exist. And the simplest representative is butadiene CH2=CH-CH=CH2. This compound is widely used in production synthetic rubber. The hydrocarbon lycopene—red crystals—was found in tomatoes and fruits. There are 13 double bonds in the carbon chain of this substance.

Ethylene for organic chemistry is, perhaps, not a brick, but a whole block. The ethylene molecule consists of two carbon atoms and four hydrogen atoms. How is ethylene built? Indeed, in all organic compounds carbon must be tetravalent, and in the ethylene molecule each carbon atom is bonded to another carbon and two hydrogens, i.e., as if trivalent.

No, there is no violation of the principle of tetravalency of carbon in the ethylene molecule: two carbon atoms are connected to each other not simply, as in ethane, but double bond. Each valency is indicated by a line, and if we connect two carbon atoms with two lines, we keep the carbon tetravalent:

But what is hidden behind such designations, how does the connection depicted by one line differ from the connection depicted by two lines?

Let's remember how the ethane molecule is formed. Around each carbon atom as a result of hybridization, i.e. mixing, averaging of one s- and three r-orbitals are formed into four completely identical hybridized ones directed in different directions sp 3-orbitals.

In the case of ethylene, the bonds between carbon atoms are constructed differently. Only two mix here r-orbitals with one orbital s. As a result, three hybridized sp 2-orbitals that lie in the same plane: two of them overlap with s-orbitals of two hydrogen atoms and bind these hydrogens to carbon, and the third orbital sp 2 overlaps with exactly the same orbital of the second carbon atom. This bond accounts for one of the lines between two carbon atoms. What does the second line symbolize?

Let's remember: we still have one more p-electron. It forms a cloud in the form of a volumetric figure eight, which is directed perpendicular to the plane of three sp 2-orbitals. These electron clouds (one eight from each carbon) can also overlap with each other, but not “head to head”, as two overlap sp 2-orbitals, but “sideways”. This overlap is indicated by the second dash. The connection of the first type (“foreheads”) is denoted by the Greek letter o (sigma), and the connection in which electron clouds

overlap “sides” is called a π-bond (and such electrons themselves are called π-electrons). All together this is a double bond. The double bond is shorter than a single bond, its length is 0.133 nm.

So, we have disassembled the structure of another part from which we can build “buildings” of organic compounds. What kind of buildings are these?

Let us first take the following combinations: one ethylene molecule and several methane molecules. If one hydrogen atom in the ethylene molecule is replaced by a methyl group (i.e., a methane residue), we obtain propylene (otherwise called propene) CH 2 = CH-CH 3.

Now let's construct the next member of the homologous series (i.e., the member with one more CH 2 group). To do this, we replace one of the hydrogen atoms in propylene with a methyl group. There are several possibilities for such substitution; as a result, we get three different butylenes (butenes).

Replacing the hydrogen of the methyl group, we arrive at normal butene-1: CH 2 =CH-CH2-CH3. Substituting hydrogen at the other end will give butene-2: CH 3 -CH=CH-CH 3 . Finally, replacing the single hydrogen at the double bond, we get iso-butylene: CH 2 = C (CH 3) 2. These are three different substances that have different boiling and melting points. The composition of all these hydrocarbons is reflected by the general formula C n N 2n. Similarly, you can derive the formulas of all possible pentenes, hexenes, etc.

So, we have learned how to obtain unsaturated hydrocarbons on paper. How do you actually get them?

Main source of protozoa alkenes(i.e., unsaturated hydrocarbons) - petroleum products, from which, after heating and distillation, ethylene, propylene, butylenes are isolated... If you heat an alkane (saturated hydrocarbon) to 500-600 ° C under high pressure in the presence of a catalyst, then two hydrogen atoms are split off to form an alkene. From n-butane, for example, produces a mixture of butene-1 and butene-2.

In the laboratory, unsaturated hydrocarbons (for example, ethylene) are obtained by removing water from alcohols; To do this, they are heated with a catalytic amount of acid:

You can also split off a hydrogen halide molecule with an alkali from halogen derivatives of saturated hydrocarbons:

The range of reactions into which compounds with a double bond enter is much more diverse and wider than the set of transformations of alkanes. Let's consider one of these reactions of unsaturated compounds.

Unsaturated substances add hydrogen halides at the double bond, and halogen-substituted saturated hydrocarbons are formed (i.e., the opposite reaction to the one just written occurs). But if you add a hydrogen halide to an unsymmetrical alkene (one that has different groups on both sides of the double bond), you can get two different derivatives, for example, in the case of propene, either CH 3 CH 2 CH 2 Cl or CH 3 CHClCH 3.

This reaction was studied by the Russian chemist V.V. Markovnikov back in the last century. He established the rule that now bears his name: a halogen attaches to the least hydrogenated carbon atom (that is, the one that is bonded to the fewest hydrogen atoms). This means that mainly chloride is formed from propylene iso-propyl CH 3 CHClCH 3 . But why does the reaction happen this way? Modern theory provides an explanation of Markovnikov's rule. We will present this theory in a somewhat simplified form.

The fact is that the mechanisms of even seemingly simple chemical reactions are quite complex and include several stages. So it is with the addition reaction of hydrogen halide. A hydrogen chloride molecule does not attach to an alkene molecule immediately, but in parts. Hydrogen is added first in the form of the H+ proton. A positively charged proton approaches a propylene molecule. Which carbon atom connected by a double bond will it attack? It turns out that it is the extreme one, because it contains a small negative charge, designated δ- (delta minus). But how did this charge, this slight excess of electron density, arise?

The metal band is "to blame" for this. It seems to push electrons away from itself, which therefore accumulate at the opposite carbon atom, away from the methyl group. Let us just emphasize once again that this shift in electron density is very small. It is much less than if a whole electron moved from the middle carbon atom to the outer one. Then we would have to put a plus over the middle atom, and a minus over the extreme one (we put the sign δ-, which means a small part of the total negative charge of the electron).

So, it is now clear that a positively charged proton will much more readily approach the outermost carbon atom, which carries some excess electron density.

A positively charged proton attaches to an uncharged molecule and transfers its charge to it. Where will this charge be located? If a proton were to attach to the middle carbon atom, a charge would appear on the outermost carbon. In fact, the proton approaches the outermost carbon atom, and the charge arises on the middle carbon.. Is there a difference where the charge is concentrated? Yes, and there is a big difference. Both carbocations (that is, organic particles that carry a positive charge on the carbon atom) are unstable and have a very short lifespan. But still, the second cation is more stable: the fact is that it is surrounded on both sides by methyl groups; and we already know that methyl groups are capable of donating electrons and repelling them from themselves. It turns out that the methyl groups partially compensate for the resulting positive charge, and the lower this charge, the more stable the carbocation. In the first case there is a positive charge. quenched by only one ethyl group, this carbocation will be less stable than the second.

As a rule, the more stable a particle is, the easier it is to form. This means that the second carbocation will be obtained much more often than the first. The second stage of the reaction is the addition of a negatively charged chlorine ion to the carbocation. Since the carbocation of the second type predominates in the products of the first stage, as a result of the entire reaction, one molecule of 1-chloropropane produces thousands of molecules of the isomer in which chlorine is attached to the middle carbon. That is why we say that the accession proceeds mainly according to the Markovnikov rule. Two factors - the site of the proton attack in the first stage and the stability of the carbocation formed after this - determine the fulfillment of this rule.

Unsaturated compounds easily attach not only hydrogen chloride, but also many other molecules. Typical examples of chemical transformations of ethylene are shown in the diagram.

The reader may have a question: are there organic molecules built only from ethylene blocks? Yes, they do exist. And the simplest representative is butadiene CH 2 =CH-CH=CH2. This compound is widely used in the production of synthetic rubber. The hydrocarbon lycopene was found in tomatoes and fruits - red crystals. There are 13 double bonds in the carbon chain of this substance.

Double bond

a covalent four-electron bond between two adjacent atoms in a molecule. D. s. usually denoted by two valence primes: >C=CC=N -, >C=O, >C=S, - N=N -, - H=O, etc. This implies that one pair of electrons with sp 2 or sp- hybridized orbitals form a σ bond (see. rice. 1 ), the electron density of which is concentrated along the interatomic axis; The σ bond is similar to a simple bond. Another pair of electrons with r-orbitals forms a π bond, the electron density of which is concentrated outside the interatomic axis. If in education D. s. atoms of group IV or V of the periodic system take part, then these atoms and the atoms directly associated with them are located in the same plane; bond angles are 120°. In the case of asymmetric systems, distortions of the molecular structure are possible. D. s. shorter than a simple bond and characterized by a high energy barrier to internal rotation; therefore, the positions of the substituents on atoms bonded by bonds are nonequivalent, and this gives rise to the phenomenon of geometric isomerism (See Isomerism). Compounds containing D. are capable of addition reactions. If D. s. is electronically symmetric, then the reactions are carried out both by radical (by homolysis of the π-bond) and by ionic mechanisms (due to the polarizing effect of the medium). If the electronegativities of the atoms bonded to the DS are different or if different substituents are bonded to them, then the π bond is highly polarized. Compounds containing polar D. are prone to addition by an ionic mechanism: to electron-withdrawing D. with. Nucleophilic reagents easily attach, and electron-donating reagents. - electrophilic. The direction of electron displacement during D. polarization. It is customary to indicate with arrows in formulas, and the resulting excess charges with symbols δ - And δ + . This makes it easier to understand the radical and ionic mechanisms of addition reactions:

In compounds with two dynamic bonds separated by one simple bond, conjugation of π-bonds takes place and the formation of a single π-electron cloud, the lability of which is manifested along the entire chain ( rice. 2 , left). The consequence of this conjugation is the ability to undergo 1,4-addition reactions:

G. A. Sokolsky.

Rice. 1. Double bond scheme >C = C

Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what “Double bond” is in other dictionaries:

Double Bond: A double bond is a chemical bond between two atoms formed by two pairs of electrons; a special case of multiple connection. Double bind (or double message) psychological concept in Gregory Bateson's theory of schizophrenia ... Wikipedia

DOUBLE BIND- En.: Double bind According to Erickson and Rossi, a double bind is a proposition of a rather simplistic and illusory choice (Erickson & Rossi, 1976, p. 62.): “Do you want to experience a deep trance or a medium one?” An alternative is proposed, but the result is... ... New hypnosis: glossary, principles and method. Introduction to Ericksonian Hypnotherapy

double bond- dvigubasis ryšys statusas T sritis chemija apibrėžtis Du kovalentiniai ryšiai tarp dviejų atomų. atitikmenys: engl. double bond; ethylene bond rus. double bond; ethylene bond ryšiai: sinonimas – dvilypis ryšys sinonimas – etileninis ryšys … Chemijos terminų aiškinamasis žodynas

double bond- dvilypis ryšys statusas T sritis fizika atitikmenys: engl. double bond vok. Doppelbindung, f rus. double bond, f pranc. liaison double, f … Fizikos terminų žodynas

Chem. bond between neighboring atoms in a molecule carried out by two pairs of electrons. Characteristic ch. arr. for organic connections. Graphically represented by two valence strokes, for example, Connections with D. s. (see, for example, Ethylene, Butenes, ... ... Big Encyclopedic Polytechnic Dictionary

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Double bond- Communication disorders observed in families of patients with schizophrenia. Communication between patients and parents takes on a multifaceted character, proceeding on two planes that are incompatible in affective terms. For example, a patient with schizophrenia, rejoicing... ... Dictionary psychiatric terms

Double bond- a violation in the sphere of communication between the child and the parent, when the child receives contradictory messages from the latter. For example, a mother, not accepting her tender feeling towards the child, repels the child with his coldness, and then expresses ostentatious love... Encyclopedic Dictionary of Psychology and Pedagogy

This term has other meanings, see Double bond. Fig. 1. Sigma connection ... Wikipedia

Books

• Double Castling by Noah Charney. Three sensational crimes in the art world that shocked Europe occurred simultaneously... Caravaggio's masterpiece disappeared from a Roman church. A legendary painting by Malevich was stolen in Paris. IN…