Chemical reactions in organic chemistry table. Types of chemical reactions in organic chemistry - Knowledge hypermarket. Polymerization and polycondensation
>> Chemistry: Types chemical reactions in organic chemistry
Reactions organic matter can be formally divided into four main types: substitutions, additions, eliminations (eliminations), and rearrangements (isomerizations). It is obvious that the whole variety of reactions of organic compounds cannot be reduced to the framework of the proposed classification (for example, combustion reactions). However, such a classification will help to establish analogies with those already familiar to you from the course. inorganic chemistry classifications of reactions occurring between inorganic substances.
As a rule, the main organic compound participating in the reaction is called the substrate, and the other component of the reaction is conditionally considered as a reagent.
Substitution reactions
Reactions that result in the replacement of one atom or group of atoms in the original molecule (substrate) with other atoms or groups of atoms are called substitution reactions.
Substitution reactions involve saturated and aromatic compounds, such as, for example, alkanes, cycloalkanes or arenes.
Let us give examples of such reactions.
In the course of a reaction, some chemical bonds are broken in the molecules of the reacting substances and others are formed. Organic reactions are classified according to the type of rupture chemical bonds in reacting particles. Of these, two large groups of reactions can be distinguished - radical and ionic.
Radical reactions are processes that go with a homolytic gap covalent bond. In a homolytic rupture, a pair of electrons forming a bond is divided in such a way that each of the formed particles receives one electron. As a result of homolytic rupture, free radicals are formed:
A neutral atom or particle with an unpaired electron is called a free radical.
Ionic reactions are processes that proceed with the heterolytic breaking of covalent bonds, when both bond electrons remain with one of the previously bound particles:
As a result of heterolytic bond cleavage, charged particles are obtained: nucleophilic and electrophilic.
A nucleophilic particle (nucleophile) is a particle that has a pair of electrons in the outer electronic level. Due to the pair of electrons, the nucleophile is able to form a new covalent bond.
An electrophilic particle (electrophile) is a particle that has an unfilled outer electronic level. The electrophile represents unfilled, vacant orbitals for the formation of a covalent bond due to the electrons of the particle with which it interacts.
In organic chemistry, all structural changes are considered relative to the carbon atom (or atoms) involved in the reaction.
In accordance with the above, the chlorination of methane by the action of light is classified as a radical substitution, the addition of halogens to alkenes as an electrophilic addition, and the hydrolysis of alkyl halides as a nucleophilic substitution.
The following types of actions are the most common.
Main types of chemical reactions
I. Substitution reactions(replacement of one or more hydrogen atoms with halogen atoms or a special group) RCH 2 X + Y → RCH 2 Y + X
II. Addition reactions RCH=CH 2 + XY → RCHX−CH 2 Y
III. Cleavage (elimination) reactions RCHX−CH 2 Y → RCH=CH 2 + XY
IV. Isomerization reactions (rearrangements)
v. Oxidation reactions(interaction with air oxygen or an oxidizing agent)
In these types of reactions listed above, there are also specialized and registered reactions.
Specialized:
1) hydrogenation (interaction with hydrogen)
2) dehydrogenation (cleavage from a hydrogen molecule)
3) halogenation (interaction with halogen: F 2, Cl 2, Br 2, I 2)
4) dehalogenation (cleavage from a halogen molecule)
5) hydrohalogenation (interaction with hydrogen halide)
6) dehydrohalogenation (cleavage from a hydrogen halide molecule)
7) hydration (interaction with water in an irreversible reaction)
8) dehydration (cleavage from a water molecule)
9) hydrolysis (interaction with water in a reversible reaction)
10) polymerization (obtaining a multiple increased carbon skeleton from identical simple compounds)
11) polycondensation (obtaining a multiple enlarged carbon skeleton from two different compounds)
12) sulfonation (interaction with sulfuric acid)
13) nitration (interaction with nitric acid)
14) cracking (reduction of the carbon skeleton)
15) pyrolysis (decomposition of complex organic substances into simpler ones under the influence of high temperatures)
16) alkylation reaction (introduction of an alkane radical into the formula)
17) acylation reaction (introduction of the -C (CH 3) O group into the formula)
18) aromatization reaction (formation of a hydrocarbon of a series of arenes)
19) decarboxylation reaction (cleavage from a molecule carboxyl group-COOH)
20) esterification reaction (reaction of alcohol with acid, or obtaining ester from alcohol or carboxylic acid)
21) the reaction of the "silver mirror" (interaction with an ammonia solution of silver oxide (I))
Nominal reactions:
1) Wurtz reaction (elongation of the carbon skeleton during the interaction of a halogenated hydrocarbon with active metal)
2) Kucherov's reaction (obtaining aldehyde by reacting acetylene with water)
3) Konovalov reaction (reaction of an alkane with dilute nitric acid)
4) Wagner reaction (oxidation of hydrocarbons with a double bond by the oxygen of an oxidizing agent in a weakly alkaline or neutral medium under normal conditions)
5) Lebedev reaction (dehydrogenation and dehydration of alcohols in the production of alkadienes)
6) Friedel-Crafts reaction (alkylation reaction of arene with chloroalkane to obtain benzene homologues)
7) Zelinsky reaction (obtaining benzene from cyclohexane by dehydrogenation)
8) Kirchhoff reaction (conversion of starch to glucose under the catalytic action of sulfuric acid)
Synopsis: "Types of chemical reactions in organic chemistry"The reactions of organic substances can be formally divided into four main types: substitution, addition, elimination (elimination) and rearrangement (isomerization). It is obvious that the whole variety of reactions of organic compounds cannot be reduced to the framework of the proposed classification (for example, combustion reactions). However, such a classification will help to establish analogies with the classifications of reactions that take place between inorganic substances already familiar to you from the course of inorganic chemistry.
As a rule, the main organic compound participating in the reaction is called the substrate, and the other component of the reaction is conditionally considered as a reagent.
Substitution reactions
Reactions that result in the replacement of one atom or group of atoms in the original molecule (substrate) with other atoms or groups of atoms are called substitution reactions.
Substitution reactions involve saturated and aromatic compounds, such as, for example, alkanes, cycloalkanes or arenes.
Let us give examples of such reactions.
Under the action of light, hydrogen atoms in a methane molecule can be replaced by halogen atoms, for example, by chlorine atoms:
CH4 + Cl2 → CH3Cl + HCl
Another example of replacing hydrogen with halogen is the conversion of benzene to bromobenzene:
With this form of recording, the reagents, catalyst, reaction conditions are written above the arrow, and the inorganic reaction products below it.
Addition reactions
Reactions, as a result of which two or more molecules of reactants combine into one, are called addition reactions.
Unsaturated compounds, such as, for example, alkenes or alkynes, enter into addition reactions. Depending on which molecule acts as a reagent, hydrogenation (or reduction), halogenation, hydrohalogenation, hydration, and other addition reactions are distinguished. Each of them requires certain conditions.
1 . hydrogenation - the reaction of adding a hydrogen molecule to a multiple bond:
CH3-CH = CH2 + H2 → CH3-CH2-CH3
propane propane
2 . Hydrohalogenation - hydrogen halide addition reaction (for example, hydrochlorination):
CH2=CH2 + Hcl → CH3-CH2-Cl
ethene chloroethane
3 . Halogenation - halogen addition reaction (for example, chlorination):
CH2=CH2 + Cl2 → CH2Cl-CH2Cl
ethene 1,2-dichloroethane
4 . Polymerization - a special type of addition reactions, during which molecules of a substance with a small molecular weight are combined with each other to form molecules of a substance with a very high molecular weight - macromolecules.
polymerization reactions - these are the processes of combining many molecules of a low molecular weight substance (monomer) into large molecules (macromolecules) of a polymer.
An example of a polymerization reaction is the production of polyethylene from ethylene (ethene) under the action of ultraviolet radiation and radical polymerization initiator R.
Types of chemical reactions in organic chemistry
Cleavage (elimination) reactions
Reactions, as a result of which molecules of several new substances are formed from the molecule of the original compound, are called cleavage or elimination reactions.
Examples of such reactions are the production of ethylene from various organic substances.
Types of chemical reactions in organic chemistry
Special meaning among the cleavage reactions, it has the reaction of thermal splitting of hydrocarbons, on which cracking (English to crack - split) of alkanes is based - the most important technological process:
In most cases, the splitting off of a small molecule from a molecule of the original substance leads to the formation of an additional p-bond between atoms. Elimination reactions proceed under certain conditions and with certain reagents. The above equations reflect only the final result of these transformations.
Isomerization reactions
Reactions, as a result of which molecules of one substance form molecules of other substances of the same qualitative and quantitative composition, that is, with the same molecular formula, are called isomerization reactions.
An example of such a reaction is the isomerization of the carbon skeleton of alkanes linear structure into branched, which occurs on aluminum chloride at high temperature:
Types of chemical reactions in organic chemistry
1 . What type of reactions are:
a) obtaining chloromethane from methane;
b) obtaining bromobenzene from benzene;
c) obtaining chloroethane from ethylene;
d) obtaining ethylene from ethanol;
e) conversion of butane to isobutane;
f) ethane dehydrogenation;
g) conversion of bromoethane to ethanol?
2 . What reactions are typical for: a) alkanes; b) alkenes? Give examples of reactions.
3 . What are the features of isomerization reactions? What unites them with the reactions of obtaining allotropic modifications of one chemical element? Give examples.
4. In which reactions (addition, substitution, elimination, isomerization) is the molecular weight of the starting compound:
a) is increasing
b) decreases;
c) does not change;
d) does it increase or decrease depending on the reagent?
During the course of chemical reactions, some bonds are broken and other bonds are formed. Chemical reactions are conventionally divided into organic and inorganic. Organic reactions are considered to be reactions in which at least one of the reactants is an organic compound that changes its molecular structure during the reaction. honors organic reactions from inorganic is that, as a rule, molecules participate in them. The rate of such reactions is low, and the yield of the product is usually only 50-80%. To increase the reaction rate, catalysts are used, the temperature or pressure is increased. Next, consider the types of chemical reactions in organic chemistry.
Classification according to the nature of chemical transformations
- Substitution reactions
- Addition reactions
- Isomerization reaction and rearrangement
- Oxidation reactions
- Decomposition reactions
Substitution reactions
During substitution reactions, one atom or group of atoms in the initial molecule is replaced by other atoms or groups of atoms, forming a new molecule. As a rule, such reactions are characteristic of saturated and aromatic hydrocarbons, for example:
Addition reactions
In the course of addition reactions, one molecule of a new compound is formed from two or more molecules of substances. Such reactions are characteristic of unsaturated compounds. There are reactions of hydrogenation (reduction), halogenation, hydrohalogenation, hydration, polymerization, etc.:
- hydrogenation– addition of a hydrogen molecule:
Elimination reaction (cleavage)
As a result of cleavage reactions organic molecules lose atoms or groups of atoms, and a new substance is formed containing one or more multiple bonds. Elimination reactions include reactions dehydrogenation, dehydration, dehydrohalogenation etc.:
Isomerization reactions and rearrangement
In the course of such reactions, intramolecular rearrangement occurs, i.e. the transition of atoms or groups of atoms from one part of the molecule to another without changing the molecular formula of the substance participating in the reaction, for example: 
Oxidation reactions
As a result of exposure to an oxidizing reagent, the degree of oxidation of carbon in an organic atom, molecule or ion increases due to the donation of electrons, as a result of which a new compound is formed: 
Condensation and polycondensation reactions
They consist in the interaction of several (two or more) organic compounds with the formation new S-S bonds and low molecular weight compounds:
Polycondensation is the formation of a polymer molecule from monomers containing functional groups with the release of a low molecular weight compound. Unlike the polymerization reaction, which results in a polymer having a composition similar to the monomer, as a result of polycondensation reactions, the composition of the formed polymer differs from its monomer:
Decomposition reactions
This is the process of splitting a complex organic compound into less complex or simple substances:
C 18 H 38 → C 9 H 18 + C 9 H 20
Classification of chemical reactions by mechanisms
The course of reactions with the breaking of covalent bonds in organic compounds possibly by two mechanisms (i.e., the path leading to the breaking of the old connection and the formation of a new one) - heterolytic (ionic) and homolytic (radical).
Heterolytic (ionic) mechanism
In reactions proceeding according to the heterolytic mechanism, intermediate particles of the ionic type with a charged carbon atom are formed. Particles that carry a positive charge are called carbocations, and a negative charge is called carbanions. In this case, there is not a break in the common electron pair, but its transition to one of the atoms, with the formation of an ion: 
Strongly polar, for example, H–O, C–O, and easily polarizable, for example, C–Br, C–I bonds show a tendency to heterolytic cleavage.
Reactions proceeding according to the heterolytic mechanism are divided into nucleophilic and electrophilic reactions. A reagent that has an electron pair to form a bond is called a nucleophilic or electron donor. For example, HO -, RO -, Cl -, RCOO -, CN -, R -, NH 2, H 2 O, NH 3, C 2 H 5 OH, alkenes, arenes.
A reagent that has an unfilled electron shell and is able to attach a pair of electrons in the process of forming a new bond. The following cations are called electrophilic reagents: H +, R 3 C +, AlCl 3, ZnCl 2, SO 3, BF 3, R-Cl, R 2 C=O
Nucleophilic substitution reactions
Characteristic for alkyl and aryl halides: 
Nucleophilic addition reactions 
Electrophilic substitution reactions
Electrophilic addition reactions 
Homolytic (radical mechanism)
In reactions proceeding according to the homolytic (radical) mechanism, at the first stage, the covalent bond is broken with the formation of radicals. Further, the formed free radical acts as an attacking reagent. Bond cleavage by a radical mechanism is characteristic of non-polar or low-polarity covalent bonds (C–C, N–N, C–H).
Distinguish between radical substitution and radical addition reactions
Radical substitution reactions
characteristic of alkanes 
Radical addition reactions
characteristic of alkenes and alkynes 
Thus, we have considered the main types of chemical reactions in organic chemistry
Categories ,Theory of substitution in aromatic compounds. Reactions of electrophilic substitution. Orientants of the 2nd kind (meta-orientants).
Substituents that have a negative inductive effect or negative both inductive and mesomeric effects direct electrophilic substitution to the meta position of the benzene ring and are called orientants of the second kind.
Organic reactions, like inorganic reactions, are divided into 3 main types:
1) substitution reaction: CH 4 + CI 2 → CH 3 CI + HCI;
2) cleavage reaction: CH 3 CH 2 Br → CH 2 = CH 2 + HBr;
3) addition reaction: CH 2 \u003d CH 2 + HBr → CH 3 CH 2 Br. ( polymerization reactions)
classify on the mechanism of breaking covalent bonds in reacting molecules.
Two ways to break covalent bonds.
1. If a common electron pair is divided between atoms, forming radicals. Radicals particles that have unpaired electrons. This disconnection is called radical (homolytic).Peculiarity This connection lies in the fact that the radicals that are formed interact with the molecules present in the reaction system or with each other.
The resulting radicals interact with the molecules present in the reaction system or with each other: CH 3 + CI 2 → CH 3 CI + CI.
According to the radical mechanism, reactions occur in which bonds of low polarity (C-C, C-H, N-N) are broken at high temperature, under the action of light or radioactive radiation.
2. If, when a bond is broken, a common electron pair remains with one atom, then ions are cation and anion. Such a mechanism is called ionic or heterolytic. It leads to the formation of organic cations or anions: 1) methyl chloride forms methyl cation and chloride anion; 2) methyl lithium forms lithium cation and methyl anion.
Organic ions enter into further transformations. In this case, the cations interact with nucleophilic("loving nuclei") particles, and organic anions - with electrophilic("loving electrons") particles (metal cations, halogens, etc.).
The ionic mechanism is observed when a polar covalent bond is broken (carbon - halogen, carbon - oxygen, etc.).
Organic ionic particles are like ions in inorganic chemistry—they have corresponding charges. However, they differ sharply: ions of inorganic compounds are present in aqueous solutions constantly, and organic ionic particles appear only at the moment of the reaction.
Therefore, in many cases it is necessary to speak not of free organic ions, but of strongly polarized molecules.
A radical mechanism is observed when a non-polar or low-polar covalent bond is broken (carbon - carbon, carbon - hydrogen, etc.).
Organic ionic particles are like ions in inorganic chemistry - they have corresponding charges.
