Types of chemical reactions in organic chemistry lesson plan in chemistry (Grade 10) on the topic. Main types of organic reactions Types of chemical reactions in organic chemistry with examples
Organic reactions can be classified into two general types.
hemolytic reactions. These reactions proceed by a radical mechanism. We will take a closer look at them in the next chapter. The kinetics and mechanism of reactions of this type were discussed in Chap. 9.
heterolytic reactions. These reactions are essentially ionic reactions. They can, in turn, be subdivided into substitution, addition, and elimination (cleavage) reactions.
Substitution reactions
In these reactions, an atom or group of atoms is replaced by another atom or group. As an example of reactions of this type, we give the hydrolysis of chloromethane with the formation of methanol:
The hydroxyl ion is a nucleophile. Therefore, the substitution in question is called nucleophilic substitution. It is denoted by the symbol SN. The substituted particle (in this case, the chlorine ion) is called the leaving group.
If we denote the nucleophile by the symbol a and the leaving group-symbol , then we can write the generalized equation for the reaction of nucleophilic substitution at the saturated carbon atom in the alkyl group R as follows:
The study of the rate of reactions of this type shows that -reactions can be divided into
Reactions of the type For some reactions of the SN type, the kinetic equation for the reaction rate (see Section 9.1) is
Thus, these reactions are first order in substrate but zero order in reactant. The kinetics characteristic of a first order reaction is a strong indication that the rate-limiting reaction step is a unimolecular process. Therefore, reactions of this type are denoted by the symbol .
The reaction has a zero order with respect to the reactant since its rate does not depend on the concentration of the reactant. Therefore, we can write:
Since the nucleophile does not participate in the rate-limiting step of the reaction, the mechanism of such a reaction must include at least two steps. The following mechanism has been proposed for such reactions:
The first stage is ionization with the formation of a carbocation. This stage is limiting (slow).
An example of type reactions is the alkaline hydrolysis of tertiary alkyl halides. For example
In the case under consideration, the reaction rate is determined by the equation
Reactions of the type For some reactions of nucleophilic substitution SN, the rate equation has the form
In this case, the reaction is first order in nucleophile and first order in . In general, it is a second order reaction. This is sufficient reason to believe that the rate-limiting step of this reaction is a bimolecular process. Therefore, the reaction of the type under consideration is denoted by the symbol. Since both the nucleophile and the substrate simultaneously participate in the rate-limiting stage of the reaction, it can be assumed that this reaction proceeds in one stage through the transition state (see Section 9.2):
Hydrolysis of primary alkyl halides in an alkaline medium proceeds according to the mechanism
This reaction has the following kinetic equation:
So far, we have considered nucleophilic substitution only at the saturated carbon atom. Nucleophilic substitution is also possible at an unsaturated carbon atom:
Reactions of this type are called nucleophilic acyl substitution.
electrophilic substitution. Electrophilic substitution reactions can also occur on benzene rings. In this type of substitution, the benzene ring supplies the electrophile with two of its delocalized α-electrons. In this case, an intermediate compound is formed - an unstable -complex of an electrophile and a leaving group. For a schematic representation of such complexes, an open circle is used, indicating the loss of two -electrons:
An example of electrophilic substitution reactions is the nitration of benzene:
The nitration of benzene is carried out in a reflux unit at a temperature of 55 to 60 °C using a nitrating mixture. Such a mixture contains equal amounts of concentrated nitric and sulfuric acids. The reaction between these acids leads to the formation of a nitroyl cation
Addition reactions
In reactions of this type, an electrophile or nucleophile is added to an unsaturated carbon atom. We will consider here one example of electrophilic addition and nucleophilic addition.
An example of electrophilic addition is the reaction between hydrogen bromide and an alkene. To obtain hydrogen bromide in the laboratory, the reaction between concentrated sulfuric acid and sodium bromide can be used (see section 16.2). Hydrogen bromide molecules are polar because the bromine atom has a negative inductive effect on hydrogen. Therefore, the hydrogen bromide molecule has the properties of a strong acid. According to modern views, the reaction of hydrogen bromide with alkenes proceeds in two stages. In the first step, the positively charged hydrogen atom attacks the double bond, which acts as a source of electrons. As a result, an activated complex and a bromide ion are formed:
The bromide ion then attacks this complex, resulting in the formation of an alkyl bromide:
An example of a nucleophilic addition is the addition of hydrogen cyanide to an aldehyde or ketone. First, the aldehyde or ketone is treated with an aqueous solution of sodium cyanide. Then, an excess amount of some mineral acid is added, which leads to the formation of hydrogen cyanide HCN. The cyanide ion is a nucleophile. It attacks the positively charged carbon atom on the carbonyl group of an aldehyde or ketone. The positive charge and polarity of the carbonyl group are due to the mesomeric effect described above. The reaction can be represented by the following scheme:
Elimination reactions (cleavage)
These reactions are the reverse of addition reactions. They lead to the removal of any atoms or groups of atoms from two carbon atoms linked by a simple covalent bond, as a result of which a multiple bond is formed between them.
An example of such a reaction is the elimination of hydrogen and halogen from alkyl halides:
To carry out this reaction, the alkyl halide is treated with potassium hydroxide in alcohol at a temperature of 60 °C.
It should be noted that the treatment of an alkyl halide with hydroxide also leads to nucleophilic substitution (see above). As a result, two competing reactions of substitution and cleavage proceed simultaneously, which leads to the formation of a mixture of substitution and cleavage products. Which of these reactions will be predominant depends on a number of factors, including the environment in which the reaction is carried out. Nucleophilic substitution of alkyl halides is carried out in the presence of water. In contrast, cleavage reactions are carried out in the absence of water and at higher temperatures.
So let's do it again!
1. During hemolytic bond cleavage, two shared electrons are distributed evenly between atoms.
2. In heterolytic bond cleavage, two shared electrons are distributed unevenly between atoms.
3. A carbanion is an ion containing a carbon atom with a negative charge.
4. A carbocation is an ion containing a carbon atom with a positive charge.
5. Solvent effects can have a significant effect on chemical processes and their equilibrium constants.
6. The influence of the chemical environment of a functional group within a molecule on the reactivity of this functional group is called the structural effect.
7. Electronic effects and steric effects are collectively referred to as structural effects.
8. The two most important electronic effects are the inductive effect and the mesomeric (resonant) effect.
9. The inductive effect is the shift of the electron density from one atom to another, which leads to the polarization of the bond between the two atoms. This effect can be positive or negative.
10. Molecular particles with multiple bonds can exist in the form of resonant hybrids between two or more resonant structures.
11. The mesomeric (resonant) effect consists in the stabilization of resonant hybrids due to the delocalization of -electrons.
12. Steric hindrance can occur when bulky groups in a molecule mechanically prevent the reaction from proceeding.
13. Nucleophile - a particle that attacks a carbon atom, supplying it with its electron pair. A nucleophile is a Lewis base.
14. Electrophile - a particle that attacks a carbon atom, accepting its electron pair. A nucleophile is a Lewis acid.
15. Hemolytic reactions are radical reactions.
16. Heterolytic reactions are mainly ionic reactions.
17. Substitution of any group in a molecule with a nucleophilic reagent is called nucleophilic substitution. The group being replaced in this case is called the leaving group.
18. Electrophilic substitution on a benzene ring involves donating two delocalized electrons to an electrophile.
19. In electrophilic addition reactions, an electrophile is added to an unsaturated carbon atom.
20. The addition of hydrogen cyanide to aldehydes or ketones is an example of nucleophilic addition.
21. In the reactions of elimination (elimination) there is a detachment of any atoms or groups of atoms from two carbon atoms linked by a simple covalent bond. As a result, a multiple bond is formed between these carbon atoms.
Municipal budgetary educational institution
"Secondary school No. 19"
Michurinsk, Tambov region
Types of chemical reactions
in organic chemistry
Golovkina Svetlana Alexandrovna,
Chemistry teacher MBOU Secondary School No. 19 in Michurinsk
Content
Abstract………………………………………………………………………….3
Introduction……………………………………………………………………………4
Test specification…………………………………………………………...5
Tests grade 9
Tests Grade 11 ……………………………………………………………………24
Information resources……………………………………………………..33
Annotation.
This paper reflects the approach of the authors to the study of types of chemical reactions in organic chemistry. The proposed material may be of interest to chemistry teachers working in basic and complete secondary schools, as it provides a generalization of the basic concepts of the types of chemical reactions in organic chemistry, which will make it possible to prepare for the GIA and the Unified State Examination and work out the material on this topic.
Introduction.
The material of organic chemistry is difficult to understand, especially in the 9th grade, where very little time is allotted for its study, with a large amount of theoretical material. Questions on organic chemistry are included in the KIM GIA and the Unified State Examination, while preparing students for the final certification, the teacher often encounters a misunderstanding of this material. It is possible to intensify the teaching process and improve the quality of mastering organic chemistry by actively using modern teaching technologies in its study, for example, the use of ICT, test control technologies. In the manual, teachers share their experience in studying small but complex material.
Specification of tests in preparation for the GIA and the Unified State Examination
Assignment of tests- evaluate the general education of students by types of chemical reactions.
Continuity of the content of the test material - show the relationship between the basic concepts of inorganic and organic chemistry.
Characteristics of the content of tests - Each version of the test control consists of three parts and tasks. Tasks of the same level of complexity and form of presentation are grouped in certain parts of the work.
Part A contains 10 tasks to choose the answer of the basic level of complexity A1, A2 .... A10
Part B contains 3 tasks to choose an answer of an increased level of complexity B1, B2, B3
Part C contains 1 task high level of complexity.
Table 1 Distribution of tasks by parts of the work.
Choice questions they check the main part of the studied material: the language of chemical science, chemical bonds, knowledge of the properties of organic substances, types and conditions of chemical reactions.
Tasks of an increased level of complexity test at an advanced level knowledge about redox reactions. The paper offers tasks with multiple choice answers.
Completing tasks of an increased level of complexity allows students to be differentiated according to their level of training and, on this basis, to give them higher marks.
Questions with a detailed answer- the most difficult in the test. These tasks test the assimilation of the following content elements: the amount of a substance, the molar volume and molar mass of a substance, the mass fraction of a dissolved substance.
4. Distribution of test tasks by content, tested skills and activities.
When determining the content of the test tasks of the control work, it was taken into account how much each of the content blocks occupies in the course of chemistry
5. Lead time
45 minutes are allotted to complete the test (1 lesson)
Approximate distribution of time allotted for the implementation of individual tasks:
for each part A task up to 2 min.
for each part B task up to 5 min.
for each part C task up to 10 min.
6. Evaluation system for individual tasks and work in general
The correct performance of each task of part A is estimated at 1 point.
The correct performance of each task of part B is evaluated by 2 points;
an error was made in one of the elements of the answer - 1 point.
Completion of the tasks of part C has a variable nature, the correct and complete fulfillment of task C1 - 4 points,
The points received by students for completing all tasks are summed up. The score is given on a five-point scale.
7. Gradation of evaluation:
0% - 25% - from the points scored "1"
26% - 50% - from the points scored "2"
51% - 75% - from the scores "3"
76% - 85% - from the scores "4"
86% - 100% - from the points scored "5"
Types of chemical reactions in organic chemistry
Chemical reaction - this is such a change in substances, in which old chemical bonds are broken and new chemical bonds are formed between the particles (atoms, ions) from which substances are built.
Chemical reactions are classified:
1. According to the number and composition of reagents and products
This type of reactions can be attributed to isomerization reactions that occur without changing not only the qualitative, but also the quantitative composition of the molecules of substances.
Decomposition reactions in organic chemistry, in contrast to decomposition reactions in inorganic chemistry, have their own specifics. They can be considered as the reverse processes of addition, since the result most often is the formation of multiple bonds or cycles.
CH3-CH2-C=-CH CH3-C=-C-CH3
ethylacetylene dimethylacetylene
In order to enter into an addition reaction, an organic molecule must have a multiple bond (or cycle), this molecule will be the main one (substrate). A simpler molecule (often an inorganic substance, a reagent) is attached at the site of a multiple bond break or ring opening. most often multiple bonds or cycles are formed.
Their distinguishing feature is the interaction of a simple substance with a complex one. The concept of "substitution" in organics is broader than in inorganic chemistry. If in the molecule of the original substance any atom or functional group is replaced by another atom or group, these are also substitution reactions.
Exchange reactions - reactions occurring between complex substances, in which their constituent parts are exchanged. Usually these reactions are considered as ionic. Reactions between ions in electrolyte solutions go almost to the end in the direction of the formation of gases, precipitation, weak electrolytes.
2. By thermal effect
Exothermic reactions proceed with the release of energy.
These include almost all compound reactions.
Exothermic reactions that proceed with the release of light are referred to as combustion reactions. The hydrogenation of ethylene is an example of an exothermic reaction. It runs at room temperature.
Endothermic reactions proceed with the absorption of energy.
Obviously, they will include almost all decomposition reactions,
CH 2 \u003d CH 2 + H 2 → CH 3 -CH 3
3. According to the use of the catalyst
They go without the participation of a catalyst.
Since all biochemical reactions occurring in the cells of living organisms proceed with the participation of special biological catalysts of a protein nature - enzymes, they all belong to catalytic or, more precisely, enzymatic ones.
4. Direction
They flow simultaneously in two opposite directions.
Most of these reactions are.
In organic chemistry, the sign of reversibility is reflected in the names - antonyms of processes:
hydrogenation - dehydrogenation,
hydration - dehydration,
polymerization - depolymerization.
All reactions are reversible esterification (the opposite process, as you know, is called hydrolysis) and hydrolysis of proteins, esters, carbohydrates, polynucleotides. The reversibility of these processes underlies the most important property of a living organism - metabolism.
Under these conditions, they flow in only one direction.
These include all exchange reactions accompanied by the formation of a precipitate, gas or a low-dissociating substance (water) and all combustion reactions.
5. According to the state of aggregation
Reactions in which reactants and reaction products are in different states of aggregation (in different phases).
Reactions in which the reactants and reaction products are in the same state of aggregation (in the same phase).
6. By changing the oxidation states of chemical elements that form substances
Reactions that take place without changing the oxidation states of chemical elements. These include, for example, all ion exchange reactions, as well as many compound reactions, many decomposition reactions, esterification reactions
Reactions that occur with a change in the oxidation states of elements. These include many reactions, including all substitution reactions, as well as those reactions of combination and decomposition in which at least one simple substance participates.
HCOOH + CH 3 OH → HCOOH3 + H2O
7. According to the mechanism of leakage.
They go between the radicals and molecules formed during the reaction.
As you already know, in all reactions, old chemical bonds are broken and new chemical bonds are formed. The method of breaking the bond in the molecules of the starting substance determines the mechanism (path) of the reaction. If the substance is formed by a covalent bond, then there can be two ways to break this bond: hemolytic and heterolytic. For example, for the molecules of Cl2, CH4, etc., a hemolytic rupture of bonds is realized, it will lead to the formation of particles with unpaired electrons, that is, free radicals.
They go between the ions already present or formed during the reaction.
Typical ionic reactions are interactions between electrolytes in solution. Ions are formed not only during the dissociation of electrolytes in solutions, but also under the action of electrical discharges, heating or radiation. Ŷ-rays, for example, convert water and methane molecules into molecular ions.
According to another ionic mechanism, reactions of addition of hydrogen halides, hydrogen, halogens to alkenes, oxidation and dehydration of alcohols, replacement of alcohol hydroxyl by halogen occur; reactions characterizing the properties of aldehydes and acids. Ions in this case are formed by heterolytic breaking of covalent polar bonds.
8. By the type of energy that initiates the reaction.
They are initiated by high-energy radiations - X-rays, nuclear radiations (Ý-rays, a-particles - He2+, etc.). With the help of radiation reactions, very fast radiopolymerization, radiolysis (radiation decomposition), etc. are carried out.
For example, instead of a two-stage production of phenol from benzene, it can be obtained by the interaction of benzene with water under the action of radiation. In this case, radicals [·OH] and [·H·] are formed from water molecules, with which benzene reacts to form phenol:
C6H6 + 2[OH] -> C6H5OH + H20
Rubber vulcanization can be carried out without sulfur using radiovulcanization, and the resulting rubber will be no worse than traditional rubber.
They are initiated by thermal energy. These include all endothermic reactions and many exothermic reactions that require an initial supply of heat, that is, the initiation of the process.
They are initiated by light energy. In addition to the above photochemical processes of HCl synthesis or the reaction of methane with chlorine, they include the production of ozone in the troposphere as a secondary atmospheric pollutant.
This type of reaction also includes the most important process that occurs in plant cells - photosynthesis.They are initiated by an electric current. In addition to the electrolysis reactions well known to you, we also indicate the reactions of electrosynthesis, for example, the reactions of the industrial production of inorganic oxidants.
Test tasks for grade 9
Option 1.
Part A
A1. What models correspond to alkene molecules?
a) all but A
b) all but B
c) all but B
d) all but G
A2. What reagent can alkanes react with:
a) Br 2 (solution)
b) Cl 2, (light)
c) H 2 SO 4
d) NaOH
A3. In the reaction of 1,3-butadiene with HCl, no
a) 3-chlorobutene-1 c) 1-chlorobutene-2
b) 4-chlorobutene-1 d) 2,3-dichlorobutane
A4. The substance with which formic acid under appropriate conditions enters into a redox reaction is:
a) copper;
b) copper (II) hydroxide;
c) copper (II) chloride;
d) copper (II) sulfate.
A5. The interaction of an ester with water can be called:
a) hydration;
b) dehydration;
c) hydrolysis;
d) hydrogenation.
A6. In a chain of transformations
reactions "a" and "b" are respectively:
a) hydration and oxidation;
b) oxidation and hydration;
c) hydration and hydration;
d) oxidation and oxidation.
A7. The reaction due to the presence of a double bond in the molecules of carbonyl compounds is the reaction:
a) joining;
b) decomposition;
c) substitution;
d) exchange.
A8. With the help of an ammonia solution of silver oxide, it is impossible to recognize:
a) ethanol and ethanal;
b) propanal and propanone;
c) propanal and glycerin;
d) butanal and 2-methylpropanal.
A9. When propenal is exposed to excess hydrogen, it forms I:
a) saturated alcohol;
b) unsaturated alcohol;
c) unsaturated hydrocarbon;
d) saturated hydrocarbon.
A10. Acetic aldehyde is formed during hydration:
a) ethane;
b) ethene;
c) ethyne;
d) ethanol.
Part B
IN 1. Match the type of reaction to the equation
TYPE OF REACTION
IN 2. Acetylene weighing 10.4 g added hydrogen chloride weighing 14.6 g. The formula of the reaction product is _____.
AT 3. Acetylene with a volume of 260 l (n.o.) was obtained from technical calcium carbide weighing 1 kg. The mass fraction of impurities (in%) contained in a sample of calcium carbide is ____ _____. (Write down your answer to the nearest hundredth).
Part C.
C 1. Write the reaction equations with which you can carry out the following
BaCl2
transformations: C O
Option 2.
Part A For each of the tasks A1-A10, four answer options are given,
only one of which is correct. Circle the answer number.
A1. Reaction characteristic of alkanes
a) accession
b) substitution
c) hydration
d) exchange
A2. Which hydrocarbons are characterized by a polymerization reaction.
a) CH
4b) C 2 H 4
c) C 6 H 6
d) C 2 H 5 OH
A3. A substance with which methane undergoes a substitution reaction.
a) CL 2 (light)
b) H 2 O
c) H 2 SO 4
d) NaOH
A4. Which substance is easily oxidized by potassium permanganate.
a) C 2 H 6
b) C 2H2
c) C 2 H 5 OH
d) C 6 H 6
A5. Which substance can be subjected to a dehydration reaction.
a) C 2 H 4
b) C 2 H 5 OH
c) CH 4
d) C H 3 COH
A6. In a chain of transformations C 2 H 6 - acetylene - ethane reactions "a" and "b" - this corresponds
a) hydration and hydrogenation
b) hydration and oxidation
c) dehydrogenation and hydrogenation
d) oxidation and hydration
A7. What is the name of the reaction of formation of esters.
a) joining
b) substitution
c) esterification
d) expansions
A8. When ethylene reacts with water, it is formed.
a) saturated alcohol
b) pure alcohol
c) saturated hydrocarbon
d) unsaturated hydrocarbon
A9. Acetic acid is formed from:
a) ethane
b) ethene
c) ethina
d) ethanol
A10. What reaction is typical for fats.
a) joining
b) oxidation
c) hydrolysis
d) substitution
Part BWhen completing tasks B1, establish a correspondence. B2 and B3 do the calculations and write down the answer.
IN 1. Set the correspondence between the type of reaction and the substance
Reaction type
IN 2. The volume of oxygen required for complete combustion is 50 liters. methane (n.c.) is equal to ___l.
AT 3. The hydrocarbon contains 16.28% hydrogen. Determine the formula of a hydrocarbon if its hydrogen vapor density is 43.
Part C. For answers to task C1, use a separate form (sheet)
Write down the number of the task and the answer to it.
C1. Calculate the amount of carbon dioxide released during the combustion of 56 liters of methane in 48 liters of oxygen
ANSWERS
Option 1
Part A
Part B
Part C
Write the reaction equations with which you can carry out the following BaCl 2
transformations: C O 2 → Na 2 CO 3 → X → CO 2. For the second process, write an ionic equation for the reaction.
Answer
Option 2
Part A
A1
Part B
Part C
Test tasks for grade 11
Option 1.
Part A For each of the tasks A1-A10, four answer options are given,
only one of which is correct. Circle the answer number.
A1. The Wurtz reaction matches the description:
1. Hydration of acetylene
2. elongation of the carbon skeleton
3. reduction of nitro derivatives with metals in an acidic environment
4. Simultaneous dehydration and ethanol dehydrogenation
A2. Glucose and sucrose can be distinguished using:
1. nitric acid
2. Ammonia solution of silver oxide
3. water
4. sodium hydroxide.
A3. Ethanol can be obtained from ethylene through the reaction
1. hydration
2. hydrogenation
3. halogenation
4. hydrohalogenation
A4. The reaction with an ammonia solution of silver oxide is typical for
1. propanol-1
2. propanal
3. propanol-2
4. dimethyl ether
A5. During alkaline hydrolysis of ethyl formate,
1. formaldehyde and ethanol
2. formic acid and ethanol
3. salt of formic acid and ethanol
4. formaldehyde and formic acid
A6. A distinctive feature of the Kucherov reaction is the interaction of substances with
1. with hydrogen
2. with chlorine
3. with water
4. with acid
A7. The Zinin reaction, characteristic of aromatic hydrocarbons, has a different name
1. chlorination
2. bromination
3. nitration
4. hydrogenation
A8. A qualitative reaction to polyhydric alcohols is their interaction
1. with copper oxide ( II)
2. with copper hydroxide ( II)
3. with copper
4. with copper oxide ( I)
A9. During the reaction of ethanol with hydrochloric acid in the presence of sulfuric acid,
1. ethylene
2. chloroethane
3. 1,2-dichloroethane
4. PVC
A10. Unlike ethanol, acetic acid reacts with
1. magnesium
2. copper hydroxide ( II)
3. Oxygenated
4. hydrogen
Part B
write them in ascending order
IN 1. The hydrolysis products of esters of the composition C 5 H 10 O 2 can be
1. pentanal and methanol
2. propanoic acid and ethanol
3. ethanol and butanal
4. butanoic acid and methanol
5. ethanoic acid and propanol
6. formaldehyde and pentanol
IN 2. interact with formic acid
1. Na 2CO3
2.HCl
3.OH
4. H 2S
5. CuSO 4
6. Cu(OH)2
AT 3. Substances with which α-aminopropanoic acid is able to interact
1. ethane
2. potassium hydroxide
3. potassium chloride
4. sulfuric acid
5. dimethyl ether
6. hydrogen chloride
Part C. For answers to task C1, use a separate form (sheet)
Write down the number of the task and the answer to it.
C1. As a result of the catalytic oxidation of propane, propionic acid with a mass of 55.5 g was obtained. The mass fraction of the yield of the reaction product is 60%. Calculate the volume of propane taken (n.o.s.).
Option 2
Part A For each of the tasks A1-A10, four answer options are given,
only one of which is correct. Circle the answer number.
A1. Under normal conditions, each of the two substances reacts with bromine water:
1. benzene and toluene
2. cyclohexane and propene
3. ethylene and benzene
4. phenol and acetylene
A2. Ethylene is formed as a result of the reaction:
1. acetylene hydration
2. chloromethane with sodium
3. acetylene with hydrogen chloride
4. ethanol dehydration
A3. Ethanol can be obtained from ethylene as a result of the reaction
1. hydration
2. hydrogenation
3. halogenation
4. hydrohalogenation
A4. As a result of the trimerization reaction of acetylene, the following is formed:
1. hexane
2. hexene
3. ethane
4. benzene
A5. During the oxidation of ethylene with an aqueous solution of KM no 4 is formed:
1. ethane
2. ethanol
3. glycerol
4. ethylene glycol
A6. During alkaline hydrolysis of 2-chlorobutane, the following are predominantly formed:
1. butanol-2
2. butanol-1
3. butanal
4. butanone
A7. Substitution reaction with chlorine enters:
1. ethene 2. ethin 3 . butene-2 4. butane
A8. A characteristic reaction for polyhydric alcohols is the interaction with:
1. H2
2. Cu
3. Ag 2 O (NH 3 solution)
4. Cu(OH)2
A9. The monomer for producing artificial rubber according to the Lebedev method is:
1. butene-2
2. ethane
3. ethylene
4. butadiene-1,3
A10. Butanol-2 and potassium chloride are formed by the interaction:
1. 1-chlorobutane and 2-chlorobutane
2. 2-chlorobutane and alcohol solution of KOH
3. 1-chlorobutane and alcohol solution of KOH
4. 2-chlorobutane and an aqueous solution of KOH
Part B When completing tasks B1-B3, select three answers and
write them in ascending order
IN 1. The hydrolysis products of esters of the composition C 6 H 12 O 2 can be
1 . ethanal and dimethyl ether
2 . propanoic acid and propanol
3 . methyl acetate and butane
4 . ethanoic acid and butanol
5. pentanoic acid and methanol
6. propanal and ethanediol
IN 2. Alkenes interact with:
1 . [ Ag(NH 3) 2 ]OH
2 . H2O
3 . Br2
4 . KMnO4(H+)
5 . Ca(OH)2
6 . Cu(OH)2
AT 3. Methylethylamine interacts with:
1 . ethane
2 . potassium hydroxide
3. hydrobromic acid
4 . oxygen
5 . propane
6 . water
Part C. For answers to task C1, use a separate form (sheet)
Write down the number of the task and the answer to it.
C1. Gaseous ammonia released by boiling 160 g of a 7% potassium hydroxide solution from 9.0 g. Ammonium chloride, dissolved in 75g of water. Determine the mass fraction of ammonia in the resulting solution.
ANSWERS
Option 1
Part A
A1
Part B
IN 1
Part C
The content of the correct answer and instructions for grading (other formulations of the answer are allowed that do not distort its meaning)
Response elements:
1. Compiled reaction equation
3C 2 H 2 
C 6 H 6
2. Determined the amount of substance acetylene and benzene
n(C 2 H 2) \u003d 10.08 / 22.4 \u003d 0.45 mol
according to the reaction equation n(C 2 H 2) : n(C 6 H 6) =3:1
n(C 6 H 6) \u003d 0.45 / 3 \u003d 0.15 mol
3. Calculated theoretical mass of benzene
m(C 6 H 6) \u003d 0.15 mol * 78 g / mol \u003d 11.7 g
4. Calculated practical mass of benzene
m(C 6 H 6) pr \u003d 0.7 * 11.7 \u003d 8.19 g
Option 2
Part A
Part B
Part C
From 1 1. Gaseous ammonia released by boiling 160 g of a 7% potassium hydroxide solution from 9.0 g. Ammonium chloride, dissolved in 75g of water. Determine the mass fraction of ammonia in the resulting solution.
Correct Answer Content and Grading Instructions Response elements:- The reaction equation is composed:
- The mass and amount of alkali substance in solution, as well as the amount of ammonium chloride substance are calculated:
- The substance that is in excess in solution is indicated:
- The mass of ammonia and its mass fraction in solution were determined
*Note. In the case when the answer contains an error in the calculations in one of the elements of the answer, which led to an incorrect answer, the mark for completing the task is reduced by only 1 point.
Informational resources.
Artemenko A.I. The wonderful world of organic chemistry. – M.: Bustard, 2004.
Gabrielyan O.S., Ostroumov I.G. Handbook of the teacher. Chemistry. 10th grade. – M.: Bustard, 2004.
Koroshchenko A.S., Medvedev Yu.N. Chemistry GIA typical test tasks - M .: "Exam", 2009.
Kuznetsova N.E., Levkina A.N., Chemistry student, grade 9. - M .: Publishing Center "Ventana - Graf", 2004.
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Many substitution reactions open the way to obtaining a variety of compounds that have economic applications. A huge role in chemical science and industry is given to electrophilic and nucleophilic substitution. In organic synthesis, these processes have a number of features that should be taken into account.
variety of chemical phenomena. Substitution reactions
Chemical changes associated with the transformations of substances are distinguished by a number of features. The final results, thermal effects may be different; some processes go to the end, in others a change in substances is often accompanied by an increase or decrease in the degree of oxidation. When classifying chemical phenomena according to their end result, attention is paid to the qualitative and quantitative differences between the reactants and the products. According to these features, 7 types of chemical transformations can be distinguished, including substitution, following the scheme: A-B + C A-C + B. A simplified record of a whole class of chemical phenomena gives an idea that among the starting substances there is a so-called "a particle that replaces an atom, ion, or functional group in a reagent. The substitution reaction is typical for limiting and
Substitution reactions can occur in the form of a double exchange: A-B + C-E A-C + B-E. One of the subspecies is the displacement, for example, of copper with iron from a solution of copper sulfate: CuSO 4 + Fe = FeSO 4 + Cu. Atoms, ions or functional groups can act as an “attacking” particle
Substitution homolytic (radical, SR)
With a radical mechanism for breaking covalent bonds, an electron pair common to different elements is proportionally distributed among the "fragments" of the molecule. Free radicals are formed. These are unstable particles, the stabilization of which occurs as a result of subsequent transformations. For example, when ethane is obtained from methane, free radicals appear that participate in the substitution reaction: CH 4 CH 3. + .H; CH 3 . + .CH 3 → C2H5; H. + .H → H2. Homolytic bond breaking according to the given substitution mechanism is of a chain nature. In methane, H atoms can be successively replaced by chlorine. The reaction with bromine proceeds similarly, but iodine is unable to directly replace hydrogen in alkanes, fluorine reacts too vigorously with them.
Heterolytic cleavage method
With the ionic mechanism of substitution reactions, electrons are unevenly distributed among the newly formed particles. The binding pair of electrons goes completely to one of the "fragments", most often, to that bond partner, towards which the negative density in the polar molecule was shifted. Substitution reactions include the formation of methyl alcohol CH 3 OH. In bromomethane CH3Br, the cleavage of the molecule is heterolytic, and the charged particles are stable. Methyl acquires a positive charge, and bromine acquires a negative one: CH 3 Br → CH 3 + + Br - ; NaOH → Na + + OH - ; CH 3 + + OH - → CH 3 OH; Na + + Br - ↔ NaBr.
Electrophiles and nucleophiles
Particles that lack electrons and can accept them are called "electrophiles". These include carbon atoms bonded to halogens in haloalkanes. Nucleophiles have an increased electron density, they "donate" a pair of electrons when creating a covalent bond. In substitution reactions, nucleophiles rich in negative charges are attacked by electron-starved electrophiles. This phenomenon is associated with the displacement of an atom or other particle - the leaving group. Another type of substitution reaction is the attack of an electrophile by a nucleophile. It is sometimes difficult to distinguish between two processes, to attribute substitution to one type or another, since it is difficult to specify exactly which of the molecules is the substrate and which is the reagent. Usually in such cases the following factors are taken into account:
- the nature of the leaving group;
- nucleophile reactivity;
- the nature of the solvent;
- structure of the alkyl part.
Substitution nucleophilic (SN)
In the process of interaction in an organic molecule, an increase in polarization is observed. In equations, a partial positive or negative charge is marked with a letter of the Greek alphabet. The polarization of the bond makes it possible to judge the nature of its rupture and the further behavior of the "fragments" of the molecule. For example, the carbon atom in iodomethane has a partial positive charge and is an electrophilic center. It attracts that part of the water dipole where oxygen, which has an excess of electrons, is located. When an electrophile interacts with a nucleophilic reagent, methanol is formed: CH 3 I + H 2 O → CH 3 OH + HI. Nucleophilic substitution reactions take place with the participation of a negatively charged ion or a molecule that has a free electron pair that is not involved in the creation of a chemical bond. The active participation of iodomethane in SN 2 reactions is explained by its openness to nucleophilic attack and the mobility of iodine.
Electrophilic substitution (SE)
An organic molecule may contain a nucleophilic center, which is characterized by an excess of electron density. It reacts with an electrophilic reagent that lacks negative charges. Such particles include atoms with free orbitals, molecules with areas of low electron density. In carbon, which has a “-” charge, interacts with the positive part of the water dipole - with hydrogen: CH 3 Na + H 2 O → CH 4 + NaOH. The product of this electrophilic substitution reaction is methane. In heterolytic reactions, oppositely charged centers of organic molecules interact, which makes them similar to ions in the chemistry of inorganic substances. It should not be overlooked that the transformation of organic compounds is rarely accompanied by the formation of true cations and anions.
Monomolecular and bimolecular reactions
Nucleophilic substitution is monomolecular (SN1). The hydrolysis of an important product of organic synthesis, tertiary butyl chloride, proceeds according to this mechanism. The first stage is slow, it is associated with gradual dissociation into carbonium cation and chloride anion. The second stage is faster, the carbonium ion reacts with water. substitution of a halogen in an alkane for an hydroxy group and obtaining a primary alcohol: (CH 3) 3 C-Cl → (CH 3) 3 C + + Cl - ; (CH 3) 3 C + + H 2 O → (CH 3) 3 C-OH + H +. The single-stage hydrolysis of primary and secondary alkyl halides is characterized by the simultaneous destruction of the carbon bond with the halogen and the formation of a C–OH pair. This is the mechanism of nucleophilic bimolecular substitution (SN2).
Heterolytic substitution mechanism
The substitution mechanism is associated with electron transfer, the creation of intermediate complexes. The reaction proceeds the faster, the easier it is to form the intermediate products characteristic of it. Often the process goes in several directions at the same time. The advantage is usually obtained by the way in which the particles that require the least energy costs for their formation are used. For example, the presence of a double bond increases the probability of the appearance of the allyl cation CH2=CH—CH 2 + , compared to the ion CH 3 + . The reason lies in the electron density of the multiple bond, which affects the delocalization of the positive charge dispersed throughout the molecule.
Benzene substitution reactions
The group for which electrophilic substitution is characteristic is arenas. The benzene ring is a convenient target for electrophilic attack. The process begins with the polarization of the bond in the second reactant, resulting in the formation of an electrophile adjacent to the electron cloud of the benzene ring. The result is a transitional complex. There is still no full-fledged connection of an electrophilic particle with one of the carbon atoms, it is attracted to the entire negative charge of the “aromatic six” of electrons. At the third stage of the process, the electrophile and one carbon atom of the ring are connected by a common pair of electrons (covalent bond). But in this case, the “aromatic six” is destroyed, which is unfavorable from the point of view of achieving a stable sustainable energy state. There is a phenomenon that can be called "proton ejection". There is a splitting of H + , a stable bond system, characteristic of arenes, is restored. The by-product contains a hydrogen cation from the benzene ring and an anion from the composition of the second reagent.
Examples of substitution reactions from organic chemistry
For alkanes, the substitution reaction is especially characteristic. Examples of electrophilic and nucleophilic transformations can be given for cycloalkanes and arenes. Similar reactions in the molecules of organic substances occur under normal conditions, but more often when heated and in the presence of catalysts. Electrophilic substitution in the aromatic nucleus is one of the widespread and well-studied processes. The most important reactions of this type are:
- Nitration of benzene in the presence of H 2 SO 4 - goes according to the scheme: C 6 H 6 → C 6 H 5 -NO 2.
- Catalytic halogenation of benzene, in particular chlorination, according to the equation: C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl.
- Aromatic proceeds with "fuming" sulfuric acid, benzenesulfonic acids are formed.
- Alkylation is the replacement of a hydrogen atom from the benzene ring with an alkyl.
- Acylation is the formation of ketones.
- Formylation is the replacement of hydrogen with a CHO group and the formation of aldehydes.
Substitution reactions include reactions in alkanes and cycloalkanes, in which halogens attack the available C-H bond. The preparation of derivatives may be associated with the substitution of one, two or all hydrogen atoms in saturated hydrocarbons and cycloparaffins. Many of the low molecular weight haloalkanes find use in the production of more complex substances belonging to different classes. The progress made in studying the mechanisms of substitution reactions gave a powerful impetus to the development of syntheses based on alkanes, cycloparaffins, arenes, and halogen derivatives of hydrocarbons.
The division of chemical reactions into organic and inorganic is rather conditional. Typical organic reactions include those in which at least one organic compound is involved, which changes its molecular structure during the reaction. Therefore, reactions in which an organic compound molecule acts as a solvent or ligand do not belong to typical organic reactions.
Organic reactions, as well as inorganic ones, can be classified according to common features into transfer reactions:
– a single electron (redox);
– electron pairs (complexation reactions);
– proton (acid-base reactions);
– atomic groups without changing the number of bonds (substitution and rearrangement reactions);
- atomic groups with a change in the number of bonds (reactions of addition, elimination, decomposition).
At the same time, the diversity and originality of organic reactions leads to the need for their classification according to other criteria:
– change in the number of particles during the reaction;
- the nature of the rupture of ties;
– electronic nature of reagents;
– the mechanism of elementary stages;
– type of activation;
- private signs;
– molecularity of reactions.
1) According to the change in the number of particles during the reaction (or according to the type of substrate transformation), the reactions of substitution, addition, elimination (cleavage), decomposition and rearrangement are distinguished.
In the case of substitution reactions, one atom (or group of atoms) in the substrate molecule is replaced by another atom (or group of atoms), resulting in the formation of a new compound:
CH 3 – CH 3 + C1 2 CH 3 – CH 2 C1 + HC1
ethane chlorine chloroethane hydrogen chloride
CH 3 – CH 2 C1 + NaOH (aqueous solution) CH 3 – CH 2 OH + NaC1
chloroethane sodium hydroxide ethanol sodium chloride
In the symbol of the substitution reaction mechanism, they are denoted by the Latin letter S (from the English “substitution” - substitution).
In the course of addition reactions, one new substance is formed from two (or several) molecules. In this case, the reagent is added via a multiple bond (C = C, C C, C = Oh S N) substrate molecules:
CH 2 = CH 2 + HBr → CH 2 Br – CH 3
ethylene hydrogen bromide bromoethane
Taking into account the symbolism of the mechanism of the processes of addition reactions, they are denoted by the letter A or the combination Ad (from the English "addition" - addition).
As a result of the elimination (cleavage) reaction, a molecule (or particle) is cleaved from the substrate and a new organic substance is formed containing a multiple bond:
CH 3 – CH 2 OH CH 2 = CH 2 + H 2 O
ethanol ethylene water
In the symbol of the mechanism of substitution reactions, they are denoted by the letter E (from the English "elimination" - elimination, splitting off).
Decomposition reactions proceed, as a rule, with the breaking of carbon-carbon bonds (C – C) and lead to the formation of two or more substances of a simpler structure from one organic substance:
CH 3 –
CH(OH) –
UNSD 
CH 3 –
CHO + HCOOH
lactic acid acetaldehyde formic acid
Rearrangement is a reaction during which the structure of the substrate changes with the formation of a product that is isomeric to the original, that is, without changing the molecular formula. This type of transformation is denoted by the Latin letter R (from the English "rearrangement" - rearrangement).
For example, 1-chloropropane rearranges to the isomeric compound 2-chloropropane in the presence of aluminum chloride as a catalyst.
CH 3 – CH 2 – CH 2 – C1 CH 3 – SNS1 – CH 3
1-chloropropane 2-chloropropane
2) According to the nature of bond breaking, homolytic (radical), heterolytic (ionic) and synchronous reactions are distinguished.
The covalent bond between atoms can be broken in such a way that the electron pair of the bond is divided between two atoms, the resulting particles receive one electron each and become free radicals - they say that homolytic splitting occurs. In this case, a new bond is formed due to the electrons of the reagent and substrate.
Radical reactions are especially widespread in the transformations of alkanes (chlorination, nitration, etc.).
With the heterolytic method of breaking a bond, a common electron pair is transferred to one of the atoms, the resulting particles become ions, have an integer electric charge and obey the laws of electrostatic attraction and repulsion.
According to the electronic nature of the reagents, heterolytic reactions are divided into electrophilic (for example, addition via multiple bonds in alkenes or hydrogen substitution in aromatic compounds) and nucleophilic (for example, hydrolysis of halogen derivatives or the interaction of alcohols with hydrogen halides).
Whether the reaction mechanism is radical or ionic can be established by studying the experimental conditions that favor the reaction.
So, radical reactions accompanied by a homolytic bond cleavage:
- are accelerated by irradiation h, under conditions of high reaction temperatures in the presence of substances that easily decompose with the formation of free radicals (for example, peroxide);
- slow down in the presence of substances that easily react with free radicals (hydroquinone, diphenylamine);
– usually take place in non-polar solvents or the gas phase;
– are often autocatalytic and are characterized by the presence of an induction period.
Ionic reactions accompanied by heterolytic bond cleavage:
– are accelerated in the presence of acids or bases and are not affected by light or free radicals;
– are not affected by free radical scavengers;
– the nature of the solvent affects the rate and direction of the reaction;
- rarely go in the gas phase.
Synchronous reactions proceed without intermediate formation of ions and radicals: the breaking of old and the formation of new bonds occur synchronously (simultaneously). An example of a synchronous response is d 
yene synthesis - Diels-Alder reaction.
Please note that the special arrow that is used to indicate the homolytic breaking of a covalent bond means the movement of one electron.
3) Depending on the electronic nature of the reagents, the reactions are divided into nucleophilic, electrophilic and free radical.
Free radicals are electrically neutral particles that have unpaired electrons, for example: Cl , NO 2, 
.
In the reaction mechanism symbol, radical reactions are denoted by the subscript R.
Nucleophilic reagents are uniatomic or polyatomic anions or electrically neutral molecules that have centers with an increased partial negative charge. These include such anions and neutral molecules as HO - , RO - , Cl - , Br - , RCOO - , CN - , R - , NH 3 , C 2 H 5 OH, etc.
In the reaction mechanism symbol, radical reactions are denoted by the subscript N.
Electrophilic reagents are cations, simple or complex molecules, which by themselves or in the presence of a catalyst have an increased affinity for an electron pair or negatively charged centers of molecules. These include cations H + , Cl + , + NO 2 , + SO 3 H, R + and molecules with free orbitals: AlCl 3 , ZnCl 2 , etc.
In the mechanism symbol, electrophilic reactions are denoted by the subscript E.
Nucleophiles are electron donors and electrophiles are their acceptors.
Electrophilic and nucleophilic reactions can be thought of as acid-base; This approach is based on the theory of generalized acids and bases (Lewis acids are an electron pair acceptor, Lewis bases are an electron pair donor).
However, one should distinguish between the concepts of electrophilicity and acidity, as well as nucleophilicity and basicity, because they are not identical. For example, basicity reflects the affinity for a proton, and nucleophilicity is most often estimated as an affinity for a carbon atom:
OH - + H + H 2 O hydroxide ion as a base
OH - + CH 3 + CH 3 OH hydroxide ion as a nucleophile
4) Depending on the mechanism of the elementary stages, the reactions of organic compounds can be very different: nucleophilic substitution S N, electrophilic substitution S E, free radical substitution S R, pairwise elimination, or elimination of E, nucleophilic or electrophilic addition of Ad E and Ad N, etc.
5) According to the type of activation, reactions are divided into catalytic, non-catalytic and photochemical.
Catalytic reactions are those reactions that require the presence of a catalyst. If an acid acts as a catalyst, we are talking about acid catalysis. Acid-catalyzed reactions include, for example, esterification reactions with the formation of esters, dehydration of alcohols with the formation of unsaturated compounds, etc.
If the catalyst is a base, then we speak of basic catalysis (as shown below, this is typical for the methanolysis of triacylglycerols).
Non-catalytic are reactions that do not require the presence of a catalyst. They only accelerate with increasing temperature, which is why they are sometimes referred to as thermal, although the term is not widely used. The starting reagents in these reactions are highly polar or charged particles. These can be, for example, hydrolysis reactions, acid-base interactions.
Photochemical reactions are activated by irradiation (photons, h); these reactions do not proceed in the dark, even with significant heating. The efficiency of the irradiation process is measured by the quantum yield, which is defined as the number of reagent molecules that reacted per one absorbed light quantum. Some reactions are characterized by a quantum yield less than unity, for others, for example, for chain reactions of alkane halogenation, this yield can reach 10 6 .
6) According to particular characteristics, the classification of reactions is extremely diverse: hydration and dehydration, hydrogenation and dehydrogenation, nitration, sulfonation, halogenation, acylation, alkylation, carboxylation and decarboxylation, enolization, closing and opening of cycles, isomerization, oxidative degradation, pyrolysis, polymerization, condensation and others
7) The molecularity of an organic reaction is determined by the number of molecules in which a real change in covalent bonds occurs at the slowest stage of the reaction, which determines its rate. There are the following types of reactions:
- monomolecular - one molecule participates in the limiting stage;
- bimolecular - there are two such molecules, etc.
Molecularity above three, as a rule, does not exist. The exception is topochemical (solid-phase) reactions.
Molecularity is reflected in the symbol of the reaction mechanism by adding the appropriate number, for example: S N 2 - nucleophilic bimolecular substitution, S E 1 - electrophilic monomolecular substitution; E1 - monomolecular elimination, etc.
Let's look at a few examples.
Example 1. Hydrogen atoms in alkanes can be replaced by halogen atoms:
CH 4 + C1 2 CH 3 C1 + HC1
The reaction proceeds by a chain radical mechanism (the attacking particle is the chlorine radical C1 ). Hence, by the electronic nature of the reagents, this is a free radical reaction; according to the change in the number of particles - the substitution reaction; according to the nature of the bond rupture - a homolytic reaction; type of activation - photochemical or thermal; on particular grounds - halogenation; reaction mechanism - S R .
Example 2. Hydrogen atoms in alkanes can be replaced by a nitro group. This reaction is called the nitration reaction and follows the scheme:
R – H + HO – NO 2 R – NO 2 + H 2 O
The nitration reaction in alkanes also follows a chain radical mechanism. Hence, by the electronic nature of the reagents, this is a free radical reaction; according to the change in the number of particles - the substitution reaction; according to the nature of the bond break - homolytic; type of activation - thermal; on particular grounds - nitration; according to the mechanism - S R .
Example 3. Alkenes easily attach a hydrogen halide to the double bond:
CH 3 – CH = CH 2 + HBr → CH 3 – CHBr – CH 3 .
The reaction can proceed according to the mechanism of electrophilic addition, which means that, according to the electronic nature of the reagents, the reaction is electrophilic (the attacking particle is H +); according to the change in the number of particles - addition reaction; according to the nature of the rupture of the bond - heterolytic; on particular grounds - hydrohalogenation; according to the mechanism - Ad E .
The same reaction in the presence of peroxides can proceed by a radical mechanism, then, due to the electronic nature of the reagents, the reaction will be radical (attacking particle - Br ); according to the change in the number of particles - addition reaction; according to the nature of the bond break - homolytic; on particular grounds - hydrohalogenation; according to the mechanism - Ad R .
Example 4. The reaction of alkaline hydrolysis of alkyl halides proceeds according to the mechanism of bimolecular nucleophilic substitution.
CH 3 CH 2 I + NaOH CH 3 CH 2 OH + NaI
Hence, by the electronic nature of the reagents, the reaction is nucleophilic (attacking particle - OH -); according to the change in the number of particles - the substitution reaction; according to the nature of the rupture of the bond - heterolytic, according to particular signs - hydrolysis; according to the mechanism - S N 2.
Example 5. When alkyl halides interact with alcoholic solutions of alkalis, alkenes are formed.
CH 3 CH 2 CH 2 Br 
[CH 3 CH 2 C + H 2] CH 3 CH =
CH 2 + H +
This is due to the fact that the resulting carbocation is stabilized not by the addition of a hydroxyl ion, the concentration of which in alcohol is negligible, but by the elimination of a proton from the neighboring carbon atom. Reaction by changing the number of particles - splitting off; according to the nature of the rupture of the bond - heterolytic; on particular grounds - dehydrohalogenation; according to the mechanism - elimination of E.
test questions
1. List the signs by which organic reactions are classified.
2. How can the following reactions be classified:
– sulfonation of toluene;
– interaction of ethanol and sulfuric acid with the formation of ethylene;
– bromination of propene;
– synthesis of margarine from vegetable oil.
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 a 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
Of particular importance among the cleavage reactions is 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 linear alkanes into branched ones, 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?
