Substitution in organic chemistry. Types of chemical reactions in organic chemistry lesson plan in chemistry (grade 10) on the topic

>> Chemistry: Types of chemical reactions in organic chemistry

Reactions of organic substances can be formally divided into four main types: substitution, addition, elimination (elimination) and rearrangement (isomerization). It is obvious that the entire 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 occurring between inorganic substances that are already familiar to you from the course of inorganic chemistry.

Typically, the main organic compound involved in a reaction is called the substrate, and the other component of the reaction is conventionally considered the reactant.

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.

The division of chemical reactions into organic and inorganic is rather arbitrary. Typical organic reactions are those that involve at least one organic compound that changes its molecular structure during the reaction. Therefore, reactions in which a molecule of an organic compound acts as a solvent or ligand are not typical organic reactions.

Organic reactions, like inorganic ones, can be classified according to general characteristics into transfer reactions:

– 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 to classify them according to other criteria:

– change in the number of particles during the reaction;

– the nature of the severance of ties;

– electronic nature of the reagents;

– the mechanism of elementary stages;

– activation type;

– private characteristics;

– molecularity of reactions.

1) Based on the change in the number of particles during the reaction (or according to the type of transformation of the substrate), reactions of substitution, addition, elimination (elimination), 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 С1 + NaOH (aqueous solution)  CH 3 – CH 2 OH + NaC1

chloroethane sodium hydroxide ethanol sodium chloride

In the symbol of the mechanism, substitution reactions are designated by the Latin letter S (from the English “substitution” - substitution).

When addition reactions occur, one new substance is formed from two (or several) molecules. In this case, the reagent is added via a multiple bond (C = S, S  S, S = 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 processes, addition reactions are designated by the letter A or the combination Ad (from the English “addition” - accession).

As a result of the elimination reaction (cleavage), a molecule (or particle) is split off from the substrate and a new organic substance containing a multiple bond is formed:

CH 3 – CH 2 OH CH 2 = CH 2 + H 2 O

ethanol ethylene water

In the symbol of the mechanism, substitution reactions are designated by the letter E (from the English “elimination” - elimination, splitting off).

Decomposition reactions proceed, as a rule, with the rupture of carbon-carbon bonds (C – C) and lead to the formation from one organic substance of two or more substances of a simpler structure:

CH 3 – CH(OH) – UNS
CH 3 – CHO + HCOOH

lactic acid acetaldehyde formic acid

Rearrangement is a reaction during which the structure of the substrate changes to form 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 into the isomeric compound 2-chloropropane in the presence of aluminum chloride as a catalyst.

CH 3 – CH 2 – CH 2 – С1  CH 3 – SNS1 – CH 3

1-chloropropane 2-chloropropane

2) Based on the nature of bond cleavage, homolytic (radical), heterolytic (ionic) and synchronous reactions are distinguished.

A 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 gain one electron each and become free radicals - they say that homolytic cleavage occurs. A new bond is formed due to the electrons of the reagent and the substrate.

Radical reactions are especially common 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.

Heterolytic reactions, based on the electronic nature of the reagents, are divided into electrophilic (for example, addition to 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 determined by studying the experimental conditions that favor the reaction.

Thus, radical reactions accompanied by homolytic cleavage of the bond:

– 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 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;

– not affected by free radical scavengers;

– the speed and direction of the reaction is influenced by the nature of the solvent;

– rarely occur in the gas phase.

Synchronous reactions occur without the intermediate formation of ions and radicals: the breaking of old bonds and the formation of new bonds occur synchronously (simultaneously). An example of a synchronous reaction is yene synthesis – Diels-Alder reaction.

Please note that the special arrow used to indicate the homolytic cleavage of a covalent bond means the movement of one electron.

3) Depending on the electronic nature of the reagents, reactions are divided into nucleophilic, electrophilic and free radical.

Free radicals are electrically neutral particles with unpaired electrons, for example: Cl ,  NO 2,
.

In the reaction mechanism symbol, radical reactions are denoted by the subscript R.

Nucleophilic reagents are mono- or polyatomic anions or electrically neutral molecules having centers with an increased partial negative charge. These include anions and neutral molecules such 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 that, by themselves or in the presence of a catalyst, have an increased affinity for electron pairs 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 represented by the subscript E.

Nucleophiles are electron donors, and electrophiles are electron acceptors.

Electrophilic and nucleophilic reactions can be thought of as acid-base reactions; This approach is based on the theory of generalized acids and bases (Lewis acids are electron pair acceptors, Lewis bases are electron pair donors).

However, it is necessary to 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 assessed as the 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, 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) Based on the type of activation, reactions are divided into catalytic, non-catalytic and photochemical.

Reactions that require the presence of a catalyst are called catalytic reactions. 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 reactions are reactions that do not require the presence of a catalyst. They only accelerate as the temperature increases, so they are sometimes called thermal, although this 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 occur 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 reacted reagent molecules per absorbed quantum of light. Some reactions are characterized by a quantum yield of less than unity; for others, for example, for chain reactions of the halogenation of alkanes, 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, cycle closure and opening, isomerization, oxidative destruction, pyrolysis, polymerization, condensation and etc.

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 speed. The following types of reactions are distinguished:

– monomolecular – one molecule participates in the limiting stage;

– bimolecular – there are two such molecules, etc.

As a rule, there is no molecularity higher than three. The exception is topochemical (solid-phase) reactions.

Molecularity is reflected in the symbol of the reaction mechanism by adding the corresponding 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 follows a chain radical mechanism (the attacking particle is the chlorine radical C1  ). This means that according to the electronic nature of the reagents, this reaction is free radical; by a change in the number of particles - a replacement reaction; by the nature of bond cleavage - homolytic reaction; activation type – photochemical or thermal; according to particular characteristics - 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. This means that according to the electronic nature of the reagents, this reaction is free radical; by a change in the number of particles - a replacement reaction; by the nature of the bond rupture - homolytic; activation type – thermal; according to particular characteristics - nitration; by mechanism – S R .

Example 3. Alkenes easily add a hydrogen halide to the double bond:

CH 3 – CH = CH 2 + HBr → CH 3 – CHBr – CH3.

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 (attack particle - H +); by a change in the number of particles – an addition reaction; by the nature of the bond rupture - heterolytic; according to particular characteristics - hydrohalogenation; by 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 (the attacking particle is Br  ); by a change in the number of particles – an addition reaction; by the nature of the bond rupture - homolytic; according to particular characteristics - hydrohalogenation; by mechanism – Ad R .

Example 4. The alkaline hydrolysis reaction of alkyl halides proceeds through the mechanism of bimolecular nucleophilic substitution.

CH 3 CH 2 I + NaOH  CH 3 CH 2 OH + NaI

This means that according to the electronic nature of the reagents, the reaction is nucleophilic (attack particle – OH –); by a change in the number of particles - a replacement reaction; according to the nature of bond cleavage - heterolytic, according to particular characteristics - hydrolysis; by mechanism – S N 2.

Example 5. When alkyl halides react 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 explained by the fact that the resulting carbocation is stabilized not by the addition of a hydroxyl ion, the concentration of which in alcohol is insignificant, but by the abstraction of a proton from the neighboring carbon atom. The reaction to change the number of particles is detachment; by the nature of the bond rupture - heterolytic; according to particular characteristics - dehydrohalogenation; according to the mechanism - elimination of E.

Control questions

1. List the characteristics 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;

– propene bromination;

– synthesis of margarine from vegetable oil.

During the reaction, some chemical bonds in the molecules of the reacting substances are broken and others are formed. Organic reactions are classified according to the type of breaking of chemical bonds in the reacting particles. From among them, two large groups of reactions can be distinguished - radical and ionic.

Radical reactions are processes that involve homolytic cleavage of a covalent bond. In homolytic cleavage, the pair of electrons forming the bond is divided in such a way that each of the resulting particles receives one electron. As a result of homolytic cleavage, free radicals are formed:

A neutral atom or particle with an unpaired electron is called a free radical.

Ionic reactions are processes that involve heterolytic cleavage of covalent bonds, when both bond electrons remain with one of the previously bonded 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 electron level. Due to a pair of electrons, a nucleophile is able to form a new covalent bond.

An electrophilic particle (electrophile) is a particle that has an unfilled outer electron level. An electrophile presents 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 under the influence of light is classified as radical substitution, the addition of halogens to alkenes as electrophilic addition, and the hydrolysis of alkyl halides as nucleophilic substitution.

The most common types of reactions are:

Basic 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. Elimination reactions RCHX−CH 2 Y → RCH=CH 2 + XY

IV. Isomerization (rearrangement) reactions

V. Oxidation reactions(interaction with atmospheric oxygen or oxidizing agent)

In these above types of reactions, they also distinguish specialized And personalized reactions.

Specialized:

1) hydrogenation (interaction with hydrogen)

2) dehydrogenation (elimination from a hydrogen molecule)

3) halogenation (interaction with halogen: F 2, Cl 2, Br 2, I 2)

4) dehalogenation (elimination from a halogen molecule)

5) hydrohalogenation (interaction with hydrogen halide)

6) dehydrohalogenation (elimination 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 (production of a multiple enlarged carbon skeleton from identical simple compounds)

11) polycondensation (obtaining a multiple enlarged carbon skeleton from two different compounds)

12) sulfonation (reaction 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 hydrocarbons of a number of arenes)

19) decarboxylation reaction (elimination of the carboxyl group -COOH from the molecule)

20) esterification reaction (the interaction of an alcohol with an acid, or the production of an ester from an alcohol or carboxylic acid)

21) “silver mirror” reaction (interaction with an ammonia solution of silver (I) oxide)

Nominal reactions:

1) Wurtz reaction (elongation of the carbon skeleton during the interaction of a halogenated hydrocarbon with an active metal)

2) Kucherov’s reaction (production of aldehyde by reacting acetylene with water)

3) Konovalov reaction (interaction of an alkane with dilute nitric acid)

4) Wagner reaction (oxidation of hydrocarbons with a double bond by oxygen of the oxidizing agent in a weakly alkaline or neutral environment under normal conditions)

5) Lebedev reaction (dehydrogenation and dehydration of alcohols to produce alkadienes)

6) Friedel-Crafts reaction (alkylation reaction of an arene with a chloroalkane to obtain benzene homologues)

7) Zelinsky reaction (production of benzene from cyclohexane by dehydrogenation)

8) Kirchhoff reaction (conversion of starch into glucose under the catalytic action of sulfuric acid)

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, Michurinsk

Content

Abstract……………………………………………………………………………….3

Introduction…………………………………………………………………………………4

Test specification………………………………………………………...5

Tests 9th grade………………………………………………………………15

Tests 11th grade…………………………………………………………………………………24

Information resources……………………………………………………..33

Annotation.

This work reflects the authors' approach to studying the types of chemical reactions in organic chemistry. The proposed material may be of interest to chemistry teachers working in primary and secondary schools, as it provides a generalization of the basic concepts of the types of chemical reactions in organic chemistry, which will allow them to prepare for the State Examination and the Unified State Exam and practice material on this topic.

Introduction.

The material of organic chemistry is difficult to understand, especially in the 9th grade, where very little time is allocated for its study, with a large amount of theoretical material. Questions on organic chemistry are included in the KIMs of the State Academy of Sciences and the Unified State Examination; when preparing students for the final certification, the teacher is often faced with a misunderstanding of this material. You can actively intensify the teaching process and improve the quality of assimilation of organic chemistry by using modern teaching technologies in its study, for example, the use of ICT, test control technologies. In the manual, teachers share their experiences when studying small but complex material.

Specification of tests for preparation for the State Examination and the Unified State Exam

Prescribing tests– evaluate the general educational training of students by types of chemical reactions.

Continuity of test material content – show the relationship between the basic concepts of inorganic and organic chemistry.

Characteristics of test content – Each version of the test control consists of three parts and tasks. Tasks of the same level of complexity and presentation form are grouped in certain parts of the work.

Part A contains 10 tasks for choosing an answer of a basic level of complexity A1, A2 .... A10

Part B contains 3 tasks for choosing an answer of increased difficulty level B1, B2, B3

PartC contains 1 task high level of complexity.

Table 1 Distribution of tasks by parts of work.

Multiple 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 difficulty They test knowledge about redox reactions at an increased level. The work offers multiple-choice tasks.

Completing tasks of an increased level of complexity allows you to differentiate students according to their level of preparation and, on this basis, give them higher grades.

Long answer questions- the most difficult in the test. These tasks test the assimilation of the following content elements: amount of a substance, molar volume and molar mass of a substance, mass fraction of a dissolved substance.

4.Distribution of test tasks according to content, skills and types of activities being tested.

When determining the content of the test tasks, the volume of each content block occupied in the chemistry course was taken into account.

5. Lead time

45 minutes are allotted for completing the test (1 lesson)

Approximate distribution of time allocated for completing individual tasks:

for each task of part A up to 2 minutes.

for each task of part B up to 5 minutes.

for each task of part C up to 10 minutes.

6. Evaluation system for individual tasks and work as a whole

Correct completion of each task in Part A is scored 1 point.

Correct completion of each task in Part B is scored 2 points;

An error was made in one of the answer elements - 1 point.

Completion of tasks in part C is variable, correct and complete completion of task C1 - 4 points,

The points received by students for completing all tasks are summed up. The rating is given on a five-point scale.

7. Gradation of assessment:

0% - 25% - from the points scored “1”

26% - 50% - from “2” points scored

51% - 75% - from the points scored “3”

76% - 85% - from the points scored “4”

86% - 100% - from the points scored “5”

Types of chemical reactions in organic chemistry

Chemical reaction - this is 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. By the number and composition of reagents and products

This type of reaction may include isomerization reactions, which 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 processes inverse to addition, since they most often result in the formation of multiple bonds or cycles.

CH3-CH2-C=-CH CH3-C=-C-CH3

ethyl acetylene dimethyl acetylene

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 added at the site where the multiple bond is broken or the ring opens.

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 organic chemistry 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 are reactions that occur between complex substances in which their constituent parts exchange places. Typically these reactions are considered ionic. Reactions between ions in electrolyte solutions proceed almost completely towards the formation of gases, precipitation, and weak electrolytes.

2. By thermal effect

Exothermic reactions occur with the release of energy.

These include almost all compound reactions.

Exothermic reactions that occur with the release of light are classified as combustion reactions. The hydrogenation of ethylene is an example of an exothermic reaction. It runs at room temperature.

3. According to the use of catalyst

They run without a catalyst.

Since all biochemical reactions occurring in the cells of living organisms occur with the participation of special biological catalysts of a protein nature - enzymes, they are all catalytic or, more precisely, enzymatic.

4. By direction

They flow simultaneously in two opposite directions.

The vast majority of such reactions are.

In organic chemistry, the sign of reversibility is reflected by the names - antonyms of the 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.