Appointment, homologous series, nomenclature of alkadienes.

Alkadieni - organic compounds, in carbohydrate aliphatic (acyclic) non-saturated character, molecules between carbon atoms have two dependent bonds, which seem to correspond to the general formula C n H 2 n -2 de n =3 or n >3. They are also called dієnovimi carbohydrates.

The simplest representative of alkadienes and propadiens.

homologous series.

The general formula of diene carbohydrates is CnH2n-2. The name alkadiene has a root, which indicates the number of atoms in the carbon of the carbon lance, and the suffix-dien (“two” “subwinning links”), which means the proximity to the given class.

C 3 H 4 - decay

C 4 H 6 - butadiene

C 5 H 8 - pentadiene

C 6 H 10 - hexadiene

C 7 H 12 - heptadiene

C 9 H 16 - nonadiene

Nomenclature of alkadienes.

1. Select the head stake. The decision to name the carbohydrate according to the IUPAC nomenclature is based on the designation of the head lancet - the found lancet of carbon atoms in the molecule. In different alkadins, it is necessary to choose the head lance in such a way that the insults of the underwires were included before the new one.

2. Numbering of atoms of the head col. The numbering of the atoms of the head lancet starts from the same cycle, which is closer to ranking for seniority (important):

multiple link → intercessor → carbohydrate radical .

Tobto. when numbering, at the designated place, name the alkadienu of the position of the multiple link may be the priority in front of the reshto.

It is necessary to number the atoms in the lances in such a rank, so that the atoms of the coal, tied with the lower links, take away the minimum numbers.

Since the position of the dependent links is not possible to designate the cob of numbering of the atoms in Lancius, it is also possible to designate the position of the intercessors like i, like for alkenives.

3. Name the mold., After the root, which denotes the number of atoms in the carbon in the lance, that suffix -dien, denotes the relevance of the link to the class of alkenes, through the names, indicate the place of rotting of the lower links in the carbonaceous lance, tobto. the number of atoms in the carbon, in which the subwire links are formed.

If there are intercessors, then name the numbers on the cob - the numbers of the atoms in the coal, for which the intercessors are known. If at each atom there are a few intercessors, then the number of the names is repeated in the name through whom (2,2-). After the numbers, through a hyphen, indicate the number of intercessors ( di- two, three- three, tetra− chotiri, penta- five) that name of the intercessor (methyl. ethyl, propyl). Potim without gaps and deficiencies in the name of the head lancer. The head lancer is called as a carbohydrate - a member of the homologous series of vlkadienes (propadiene, butadiene, pentadiene thinly).

Alkadieni- not rich in carbohydrates, two sublinks are included in the warehouse. Zagalna formula alkadiniv C n H 2n-2.

If there are sub-links between two coal-bearing lancets, or there are more atoms in the coal, then such links are called insulating. The chemical powers of such divisions do not change with alkenes, only 2 bonds enter into the reaction, and not one.

How are the sub-links divided into one σ - with a sound, then tse - with the receipt of a sound:

Yakshcho dien looks like this: C=C=C, then such a link is cumulative, and dien is called - allen.

Budova alkadiniv.

π -electronic haze of undercurrent links intersect between themselves, satisfying the unity π - Khmara. In the case of obtaining systems, electrons are delocalized for all carbon atoms:

Chim dosha molecule, tim won stiykisha.

Isomerism of alkadienes.

For dіenіv characteristic isomeria of the carbonaceous skeleton, isomeria of the position of the underwire links, and expanse of isomeria.

Physical power of alkadins.

Butadiene-1,3 is a gas that is easy to digest, with an unpleasant odor. And isoprene is homeland.

Otrimannya dіenіv.

1. Dehydrogenation of alkanes:

2. Reaction Lebedev(one-hour dehydration and dehydration):

Chemical power of alkadienes.

Chemical dominance of alkadiene in the minds of the presence of dependent links. The reaction of arrival can occur in two directions: 1.4 and 1.2 - arrival. For example,

Diapers from insulated ties

If the lower links are separated from the carbon lance between two or more single links (for example, pentadiene-1,4), such lower links are called insulating. Chemical dominance of alkadins with isolated sub-links does not differ from the dominance of alkenes with thin margins, which can involve not one, but two sub-links independently of one in the reaction.

CH 2 \u003d CH - CH 2 - CH \u003d CH 2 pentadiene-1.4

CH 2 \u003d CH - CH 2 - CH 2 - CH \u003d CH 2 hexadiene-1.5

Dієni zі with received calls

For example, sub-links are separated in Lancuse with only one single s-link, they are called successive. The most important representatives of the successful divisions:

CH 2 \u003d CH - CH \u003d CH 2 butadiene-1,3 (divinil)

2-methylbutadiene-1,3 (izoprene)

Dіeni with cumulative links

It is also necessary to establish divisions from the system Z = Z = Z, the titles of alenes - the chain link is changed from one carbon atom, such a chain link is called cumulative. For example:

The first member of the homologous series is propadiene (allene) CH 2 \u003d C \u003d CH 2: barless gas s t n l \u003d -136.2 ° С і t kіp \u003d -34.5 ° С.

H 2 C \u003d C \u003d CH - CH 2 - CH 3 pentadiene-1.2

Budova received alkadins

In the resulting dynahs of p-electron gloom, the underlying links intersect between themselves, and they create a single π-electron gloom. In the resulting system, p-electrons no longer lie on the same bonds, the stench is delocalized in all atoms, so the structure of divisions can be depicted as follows (on the basis of butadiene):

The dotted lines show the area of ​​decalization of electrons and indicate the intermediate order of the link between C - W and C = C. The succession line can include a large number of dependent links. Chim won't do it, it's more on the right side of p-electrons and it's a stikish molecule.

Isomeriya and nomenclature

For alkadienes, the same type of isomerism is characteristic, as for alkenes:

1) isomerism of the carbonaceous skeleton;

2) isomeria of the base of the underwire links;

3) cis-trans-isomeria.

Nomenclature

The head lancet at the dienakh is chosen in such a way that the faults of the underbelly links are mitigated, and numbered from that end, if the sum of the numbers of the position of the underwire links is minimal. The name of a viable alkane ends -an is replaced by -dien.

Physical power

Butadiene-1,3 is a gas that is easy to digest, with an unpleasant odor. Izoprene - home from t bale 34 °C.

Otrimannya

Butadiene-1,3

1. Dehydration and dehydration of ethanol - Lebedev's reaction

2. Dehydration n. butane

Isoprene

Dehydrogenation to 2-methylbutane

Chloroprene (2-chlorobutadiene-1,3)

Dimerization of acetylene and hydrochlorination of vinyl acetylene, which are dissolved.

1st stage:

2nd stage:

Chemical power

For alkadienes, the characteristic reaction is the electrotrophic addition of AE, which is powerful in alkenes. The most important may be the days with the resulting bonds, the shards of stench with syrovina for the extraction of rubbers. In the chemical behavior of these differences, there are special features, a smartness in the presence of molecules of success. The peculiarity of the obtained reactions is due to the fact that two dependent links in their molecules function as a single unit, so the reaction can proceed in two directions: a) up to one of the dependent links (1,2-addition) the position of the received system with the adoption of a new sub-link at the center of the system (1,4-admission).

1. Reactions coming

So, adding bromine to butadiene can produce up to two products:

1,2-admission

CH 2 \u003d CH - CH \u003d CH 2 + Br 2 → CH 2 \u003d CH - CHBr - CH 2 Br

1,4-admission

CH 2 \u003d CH - CH \u003d CH 2 + Br 2 → BrCH 2 - CH \u003d CH - CH 2 Br

The choice of reagents and minds of the reaction allows you to directly apply on the skin in two directions.

2. Polymerization reactions (synthetic rubbers are dissolved)

2. The most important power of the divisions is the building up to polymerization, as a victory for the production of synthetic rubbers. When polymerizing butadiene-1,3, as it flows like 1,4-addition, butadiene rubber is removed:

nCH 2 \u003d CH - CH \u003d CH 2 → (-CH 2 - CH \u003d CH - CH 2 -) n

The choice of organometallic catalysts in this reaction allows the use of rubber with regular household water, in which case the lancet can cis- Configuration. A similar reaction with isoprene gives synthetic isoprene rubber, which is close to natural rubber in terms of its power:

nCH 2 \u003d C (CH 3) - CH \u003d CH 2 → (-CH 2 - C (CH 3) \u003d CH - CH 2 -) n

Zastosuvannya

The main area of ​​stosuvannya alkadiene - rubber synthesis.

Rubbers

Dienov in carbohydrates are polymerized and copolymerized with different vinyl monomers with approved rubbers, which in the process of vulcanization have different grades of gum.

Lecture №14

· Alkadieni. Classification, nomenclature, types of divisions. Budova 1,3-dієnіv: obtaining p-links, understanding about the delocalization of links, finding boundary structures for the description of butadiene, akіsnі criteria їх vіdnosnogo contribution, energіya spoluchennya. Physical power of the obtained alkadins, their spectral characteristics and methods of identification.

· Methods for obtaining results: Lebedev's method, dehydration of alcohols, with butane-butene fraction of naphtha.

Dієni - spoluky, scho to avenge the molecule of two subwine carbon-coal ligaments. The main formula is homologous to the CnH2n-2 series.

Fallow in the form of roztashuvannya subvіynyh charcoal-coal svyazkіv, dієni divide into three groups:

1) dієni with cumulative (adjacent) linkages, for example, CH 2 \u003d C \u003d CH 2 (disappearing, allen);

2) dієni z pov'yazanimi subvіynimi zvez'yazkami, for example, CH 2 =CH-CH=CH 2 (butadiene-1,3);

3) dієni with insulated subwiring links, for example, CH 2 \u003d CH-CH 2 -CH \u003d CH 2 (pentadien-1.4).

Dієni with cumulative dependent bonds є іsomers of alkynіv (for example, propіn and propadієn), like stench transform when heated in the presence of meadows.

Dієni іz іzolovanymi zv'yazkami for іє budovoyu and khіmіchnimi vlastivnosti practically do not vіdznyayutsya vіd alkenіv. Їх characteristic reactions of electrotrophic adsorption, which can pass in stages.

The greatest theoretical and applied significance may be obtained.

For starters, in organic chemistry, systems with bonds linked by bonds are called such molecules, in which multiple bonds are separated by one simple link. The simplest of these systems is butadiene-1,3 or C4H6. Vyhodyachi z vykladeny earlier vyavleny about the life of a single, podvіyny and potrynyy zv'yazku, budova butadієnu did not look folding. Chotiri atomi vugletsyu to be found in sp 2-hybridized steel and bonded with three sucid atoms with s-bonds. In addition, the overlap of non-hybridized 2 R-orbitals between C-1 and C-2, as well as between C-3 and C-4 atoms of carbon lead to the establishment of two p-links.

However, the butadiene molecules are significantly foldable. It has been established that the atoms of coal and water lie near one flat, and they also change all s-strings. Non-hybridized p-orbitals are perpendicular to the central plane. Stand between C-1 and C-2 carbons, and between C-3 and C-4 atoms, 0.134 nm thick, three times more for the length of the ligament in ethylene (0.133 nm), and stand between C-2 atoms and C-3, which is 0.147 nm, is significantly less s-link in alkanes (0.154 nm).

Rice. 14.1. Dovzhina zv'yazkiv (a), perekrivannya R-orbitals (b) and delocalized MO (c) butadiene-1,3 molecules

Experimental data showed that butadiene-1,3 stykish was not evaluated. The energy of non-existent fields is often estimated by the heat of hydrolysis. Admission of a water molecule to a sub-coal-carbonaceous bond, tobto. the transformation of the unencumbered z'єdnannya into nasichene, accompanied by visions of warmth. When hydrogenating an insulated hinged bond, the bond is seen to be close to 127 kJ/mol. Also, with the hydrogenation of two subfolding bonds, the following was observed to be 254 kJ / mol. The very layers of heat are seen during hydrolysis of pentadiene-1.4 - from insulated underwires. The hydrogenation of butadiene-1,3 gave no result. The heat of hydrogenation was found to be less than 239 kJ/mol, while at 15 kJ/mol it was less than estimated. Tse means that butadiene revenge less energy (stіykіshiy), lower ochіkuvalos.

The experimental facts can be explained only by the peculiarities of the existence of butadiene (that and in the beginning of the received divisions).

Alkanes, alkenites and alkynes were induced for the localization of bonds. Such a bond is established when two atomic orbitals (AT) are recurved, and the molecular orbital that is established, links (MO) with two centers and two nuclei.

Some speeches have a twist R-orbitals of dekilkoh atoms make up a sprinkling of MO, which shove over two atoms. I would like to talk about delocalized links, which are typical for successful systems.

To explain the increased stability and non-standard lengths of bonds in the butadiene-1,3 molecule, take a look at chotiri sp 2-hybridized atom and carbon, which is in any given day.

In classical chemical formulas, a skin mark means a localized chemical link, that is. a couple of electronics. The links between the first and the other, as well as the third and fourth carbonic atoms, are designated as a subwinkle, and between the other and the third carbonic atoms, as a single one (structure A). Recurve R-orbitals, which make two p-links until dissolved, is shown in fig. 14.1.a.

Such a view is absolutely not worthy of the fact that R-electron atoms C-2 and C-3 can also be twisted. Such a relationship is shown for the additional offensive formula B:

The arc indicates a formal link between the first and fourth carbons of the diene fragment. The description of the butadiene molecule of the formula B allows us to explain the change in the long link Z-2 - C-3. However, the simplest geometric patterns show that you can see between the first and fourth atoms with a carbon of 0.4 nm, which significantly exceeds the length of a simple link.

Some descriptions of structural formulas on the paper arc of the overlaps - valence drawings show less localization of bonds, - L. Pauling, having propagated the concept of covalent bonds and the sound image of molecules, the so-called theory of resonance (method of valence schemes).

The main ambush of the concept:

· If a molecule cannot be correctly represented by one structural formula, then for it a set of boundary (canonical, resonant) structures is described.

· A real molecule cannot but be adequately represented by the same boundary structures, but by its superposition (resonant hybrid).

· A real molecule (resonant hybrid) is stable, without resonant structures. Increased stability of a real molecule is called the energy of production (delocalization, resonance).

When writing boundary structures, follow these steps:

· The geometry of nuclear changes in boundary structures can be the same. Tse means that the writing of the canonical structures can be changed more or less by the distribution of electrons p-, and ale s s- links.

· All canonical structures may be “Lewis structures”, so, for example, carbon cannot be pentavalent.

· All the atoms that take part in the couple are guilty of lying in the same plane or close to the same plane. Umov’s coplanarity of wiklikana the need for maximum overlap p-orbitals.

· Usі boundary structures due to the same number of unpaired electrons. Therefore, the biradical formula Г butadiene is not canonical.

Below are the boundary structures of butadiene (A and B) and their superposition. The dotted line shows the decolization of p-electrons, that is. that in a real molecule the p-electron gap is changed between 1 and 2, 3 and 4 carbon atoms, and between 2 and three carbon atoms.

The more stable the canonical structure, the greater the contribution to the real molecule. Boundary structures are fiction, but it is possible, but in reality, the distribution of p-electrons. Also, "the stability of the boundary structure" is the stability of fiction, and not the molecules that reality has.

Irrespective of those that the boundary structures do not reflect to the objective reality, this pidkhid seems to be even more intimidating for the understanding of the existence of power. The "contribution" of boundary structures to the actual production of p-electrons is proportional to their stability. Such an assessment will be easier under the hour of breaking the coming rules:

1) the greater the world of charge separation, the less stability of the structure;

2) structures that carry separate charges, less stable, lower neutral;

3) structures that can have more than 2 piles should not make any contribution to the pair;

4) the most efficient structures that carry the same charge on the suture atoms;

5) the greater the electronegativity of the atom, which carries a negative charge, the stronger the structure;

6) damage to the ligaments of the bonds and the valence ducts to reduce the stability of the structure (div. structure B, designated higher);

7) more stability can be a boundary structure that can have more ties.

The variation of these rules allows for rigidity, although formally the ethylene molecule can be described by two boundary structures M and H (div. below), the introduction of the H structure with separation charges of the fine grains, which can be excluded from a glance.

Special attention should be paid to vikoristana for the transition between the boundary structures of the two-string, so-called. "resonant" arrow. Such a sign is evidence of the fictitiousness of image structures.

The most rude pardon is to win when describing the boundary structures of two arrows that are single-straight at the opposite side, which indicate a reversal reaction. Such a rude pardon is to win when describing an equally important process, tobto. really basic molecules, "resonant" arrows.

In this way, the molecule of butadiene for the success of R-orbitals of chotyroh carbon atoms are expected to move the p-electron thicket between other and third carbon atoms. It is necessary to bring to deakoj double bonding of C-2 and C-3, which is shown in the change in the bond to 0.147 nm, equal to the bond of the simple bond of 0.154 nm.

To characterize the bond in organic chemistry, it is often necessary to understand the "order of the bond", which is expressed as the number of covalent bonds between atoms. The bonding order can be reversed using different methods, one of which is the difference between atoms and the same bonding with the bonds of ethane (the order of the carbon-coarse bond is more advanced 1), ethylene (the bond order is 2) (order zvyazku 3). In butadiene-1.3 links 2 -3 3 may have an order of 1.2. Such a meaning indicates that this link is closer to an ordinary one, the protea of ​​the double link is present. The order of calls is Z 1 -Z 2 and Z 3 -Z 4 dovnyuє 1.8. In addition, the most recent results explain the high stability of butadiene, which is shown by the low value of the heat of hydrogenation (a difference of 15 kJ / mol - the energy of the obtained).

In organic chemistry, daily (delocalization) accepts as a stabilizing one, tobto. reducing the energy of the molecule, factor.

Catalytically awakening water comes to 1,2 and 1,4 positions:

4.4.2. Halogenation

The halogens are also allowed to reach the 1,2- and 1,4-position systems, moreover, the amount of the 1,4-product lies in the form of a diene in carbohydrates, which causes the reaction of the halogen. The product 1,4-advance growth at elevated temperatures (up to the midpoint) and during the transition from chlorine to iodine:

Like in the case of ethylene spoluks, it can be applied both for the ionic and for the radical mechanism.

With the ionic mechanism of addition, for example to chlorine, the π-complex (I) is converted into a cob vinica π-complex (I) quickly transforms into a carbenium-chloronium ion with a positive charge on Z 2 and Z 4, which can be represented by two boundary formulas (II) or one mesomeric formula (III) . The cei ion adjoins the anion to chlorine to position 2 and 4 with the approved products 1,2- and 1,4-addition. Stay, at your quarters, you can isomerize in the same minds alone in the next to the reach I will become jealous through that very intermediate carbonic ion:

In the minds of the reaction, the system is close to becoming equal, but the skin isomer in the products of the reaction lies in the position of equal. Sound the 1,4-product energetically viable and more important.

Navpaki, if the system is far from becoming jealous, the 1,2-product can become more important, because the activation energy of the reaction of the first solution is lower, the lower the reaction is to illuminate the 1,4-product. So, in the case of addition of chlorine to divinil, the quantity of 1,2- and 1,4-dichlorobutenes is approximately equal, in the case of addition of bromine, it appears close to 66% of the 1,4-product, bonds C-C1 and equal to bromide are easier to reach. The temperature increase brings the system closer to the equal value.

With a radical addition of a halogen atom, a radical is formed, which also can lead to a reaction, however, a more important 1,4-adduct is established:

4.4.3. Hydrohalogenation

The reactions of adding hydrogen halides have the same regularities:

4.4.4. Hypohalogenation

Hypohalogenic acids and their ethers are more importantly added to the 1,2-position. Here the system at the time of the reaction is especially far away from becoming equal (the C-O link is significantly lower than the C-Hlg link), and the activation energy in the reaction of 1.2 is lower to the product, lower in the reaction of 1.4 to the product:

4.4.5. Dimerization of divisions

When heated, the molecules of the diene carbohydrates are joined one to one in such a way that one of them reacts in 1.2, and the other in 1.4 positions. At the same time, in small quantities, the product of the advent of both molecules in 1.4 positions enters:

Molecules of various divisions can enter into such a dimerization reaction:

4.4.6. Dinenovy synthesis

It is especially easy for such a reaction to occur in that case, if one of the reacting molecules can not activate dependent links, the electricality of such a reaction is promoted by electronegative atoms. Similar condensations took away the name diene synthesis or Diels reaction-Aldera:

This reaction is widely used for the acidic and calciferous purposes of diene carbohydrates, as well as for the synthesis of various derivatives from six-membered cycles.

Reactions of diene synthesis and dimerization of alkadienes go through a cyclic transitional camp with one-hour or maybe one-hour resolution of both new bonds, that is, recyclical process.

Possibility of mind that a similar kind of cyclization reactions can take place without intermediate resolution of radicals or ions, according to the laws that can be named Woodworth rules-Hoffmann. According to these rules, in order to close the cycle, the orbitals, which establish new links, are due to the mother's ability to overlap with the established orbitals, which link, that is due to buti being straightened one to one by segments of the same sign.

Although it is not necessary to damage the molecules (transition of electrons into a larger high level from the change of sign of the segments), the process of permissions according to the symmetry is thermal, i.e., the reaction takes time to sag when heated. However, for the designated orientation of the orbitals, it is necessary to transfer the electrons of one of the molecules to a higher level (to the orbital that expands), the reaction is allowed according to the symmetry only as a photochemical process.

Zrozumilo, such reactions can go and radical or catalytic mechanisms for the resolution of intermediate particles. Prior to such processes, the Woodworth-Hoffmann rules cannot be extended.