Example 2.2.

Write the structural formula for the compound 2,4,5 trimethyl-3-ethylhexane. Write the gross formula of this compound.

1. The main (the longest carbon chain) is recorded, i.e. the carbon skeleton of the alkane at the end of the proposed name is written. In this example, it is hexane and all carbon atoms are numbered:

C - C - C - C - C - C

2. In accordance with the numbers indicated in the formula, all substituents are placed.

C - C - C - C - C - C

CH 3 C 2 H 5 CH 3 CH 3

3. Observing the conditions of tetravalence of carbon atoms, fill the remaining free valencies of carbon atoms in the carbon skeleton with hydrogen atoms:

CH 3 - CH - CH - CH - CH - CH 3

CH 3 C 2 H 5 CH 3 CH 3

4. The number of carbon atoms in a given compound 11. The empirical formula of this compound is C 11 H 24

Isomerism of alkanes. Derivation of structural formulas of isomers.

Molecules that have the same composition but differ in different structures are called isomers. Isomers differ from each other in chemical and physical properties.

There are several types of isomerism in organic chemistry. Limiting aliphatic hydrocarbons - alkanes have one character, the simplest type of isomerism. This type of isomerism is called structural or carbon skeleton isomerism.

In the molecules of methane, ethane and propane, there can be only one single order of connection of carbon atoms:

N N N N N

│ │ │ │ │ │

N - C - N N - C - C - N N - C - C - C - N

│ │ │ │ │ │

N N N N N

Methane ethane propane

If a hydrocarbon molecule contains more than three atoms, then the order of their connection to each other can be different. For example, C 4 H 8 butane may contain two isomers: linear and branched.

Example 2.3. Compose and name all possible isomers of C 5 H 12 pentane.

When deriving the structural formulas of individual isomers, one can proceed as follows.

1. According to the total number of carbon atoms in a molecule (5), I first write down a straight carbon chain - a carbon skeleton:

2. Then, “cleaving off” one extreme carbon atom, arrange them at the remaining carbons in the chain so as to obtain the maximum possible number of completely new structures. With the elimination of one carbon atom from pentane, only one more isomer can be obtained:

3. It is impossible to get another isomer by rearranging the carbon "taken out" from the chain, since when rearranging it to the third carbon atom of the main chain, according to the rules for naming, the numbering of the main chain will need to be done from right to left. By removing two carbon atoms from pentane, another isomer can be obtained:

4. Observing the conditions of tetravalence of carbon atoms, fill the remaining free valencies of carbon atoms in the carbon skeleton with hydrogen atoms

(See example 2.2.)

Note: it must be understood that by "bending" a molecule arbitrarily, a new isomer cannot be obtained. The formation of isomers is observed only when the original structure of the compound is disturbed. For example, the following connections

C - C - C - C - C and C - C - C

are not isomers, they are the carbon skeleton of the same pentane compound.

3. CHEMICAL PROPERTIES OF LIMITED HYDROCARBONS

(tasks №№ 51 - 75)

Literature:

N.L. Glinka. General chemistry. - L .: Chemistry, 1988, ch.XV, p. 164, p. 452-455.

Example 3.1. Using pentane as an example, characterize the chemical properties of alkanes. Specify the reaction conditions and name the reaction products.

Solution:

1. The main reactions of alkanes are hydrogen substitution reactions proceeding according to the free radical mechanism.

1.1. Halogenation h n

CH 3 - CH 2 - CH 2 - CH 2 - C H 3 + Cl 2 ¾¾® CH 3 - CH 2 - CH 2 - CH 2 - CH 2 Cl + HCl

pentane 1-chloropentane

CH 3 - C H 2 - CH 2 - CH 2 - CH 3 + Cl 2 ¾¾® CH 3 - CH - CH 2 - CH 2 - CH 3 + HCl

2-chloropentane

CH 3 - CH 2 - C H 2 - CH 2 - CH 3 + Cl 2 ¾¾® CH 3 - CH 2 - CH - CH 2 - CH 3 + HCl

3-chloropentane

At the first stage of the reaction in the pentane molecule, the substitution of the hydrogen atom will occur both at the primary and at the secondary carbon atom, resulting in the formation of a mixture of isomeric monochlorine derivatives.

However, the binding energy of a hydrogen atom with a primary carbon atom is greater than with a secondary carbon atom and greater than with a tertiary carbon atom, so the replacement of the hydrogen atom associated with the tertiary carbon atom is easier. This phenomenon is called selectivity. It is more pronounced in less active halogens (bromine, iodine). As the temperature rises, the selectivity decreases.

1.2. Nitration (reaction of M.M. Konovalov)

HNO 3 \u003d OHNO 2 Catalyst H 2 SO 4 conc.

As a result of the reaction, a mixture of nitro derivatives is formed.

t \u003d 120-150 0 С

CH 3 - CH 2 - CH 2 - CH 2 - C H 3 + OHNO 2 ¾¾® CH 3 - CH 2 - CH 2 - CH 2 - CH 2 NO 2 + H 2 O

pentane 1-nitropentane

t \u003d 120-150 0 С

CH 3 - C H 2 - CH 2 - CH 2 - CH 3 + OHNO 2 ¾¾® CH 3 - CH - CH 2 - CH 2 - CH 3 + H 2 O

NO 2 2-nitropentane

t \u003d 120-150 0 С

CH 3 - CH 2 - C H 2 - CH 2 - CH 3 + OHNO 2 ¾¾® CH 3 - CH 2 - CH - CH 2 - CH 3 + H 2 O

NO 2 3-nitropentane

1.3. Sulfonation reaction Concentrated H 2 SO 4 \u003d OHSO 3 H

CH 3 - CH 2 - CH 2 - CH 2 - C H 3 + OHSO 3 H ® CH 3 - CH 2 - CH 2 - CH 2 - CH 2 SO 3 H + H 2 O

pentane 1-sulfopentane

2. The reaction of complete oxidation - combustion.

C 5 H 12 + 8 (O 2 + 3.76 N 2) ® 5CO 2 + 6H 2 O + 8 × 3.76N 2

3. Thermal decomposition

C 5 H 12 ® 5C + 6H 2

4. Cracking - a cleavage reaction with the formation of an alkane and an alkene

CH 3 - CH 2 - CH 2 - CH 2 - CH 3 ¾¾® CH 3 - CH 3 + CH 2 \u003d CH - CH 3

pentane ethane propene

5. Isomerization reaction

CH 3 - CH 2 - CH 2 - CH 2 - CH 3 ¾¾® CH 3 ¾ C ¾ CH 3

CH 3 2,2-dimethylpropane

Example 3.2. Describe the methods of obtaining alkanes. Write the reaction equations that can be used to produce propane.

Solution:

1. Cracking of alkanes

CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 3 ® CH 3 - CH 2 - CH 3 + CH 2 \u003d CH - CH 3

hexane propane propene

2. Wurtz reaction

CH 3 - Cl + 2Na + Cl - CH 2 - CH 3 ® CH 3 - CH 2 - CH 3 + 2NaCl

chloromethane chloroethane propane

3. Recovery of halogenated alkanes

3.1. Hydrogen reduction

CH 3 - CH 2 - CH 2 - I + H - H® CH 3 - CH 2 - CH 3 + HI

1-iodopropane hydrogen propane

3.2. Recovery with hydrogen halide

CH 3 - CH 2 - CH 2 - I + H - I® CH 3 - CH 2 - CH 3 + I 2

1-iodopropane iodo-propane iodine

fusion

CH 3 - CH 2 - CH 2 - C \u003d O + NaOH ¾¾¾® CH 3 - CH 2 - CH 3 + Na 2 CO 3

sodium salt \ hydroxide propane carbonate

butanoic acid ONa sodium sodium (soda)

5. Hydrogenation of unsaturated hydrocarbons

5.1. Hydrogenation of alkenes

CH 2 \u003d CH - CH 3 + H 2 ® CH 3 - CH 2 - CH 3

propane propane

5.2. Alkyne hydrogenation

CH º C - CH 3 + 2H 2 ® CH 3 - CH 2 - CH 3

Task.

Complex organic formulas are quite laborious in drawing them with the usual WORD methods. To solve this problem, special chemical editors have been created. They differ in specialization and their capabilities, in the degree of complexity of the interface and work in them, etc. In this lesson, we should get acquainted with the work of one of these editors by preparing a document file with the necessary formulas.

General characteristics of the ChemSketh editor

Chemical Editor ChemSketch from the ACD / Labs software package of the Canadian company "Advanced Chemistry Development" in terms of functionality is not inferior to the ChemDraw editor and even surpasses it in some ways. Unlike ChemDraw (memory size 60 megabytes), ChemSketch takes up only about 20 megabytes of disk space. It is also important that the documents created using ChemSketch take up a small amount - only a few kilobytes. This chemical editor is more focused on working with organic formulas of an average level of complexity (there is a large library of ready-made formulas), but it is also convenient to create chemical formulas in it. organic matter. It can be used to optimize molecules in three-dimensional space, calculate distances and bond angles between atoms in molecular structure and much more.

The chemical formula editor for xumuk.ru was written in 20 days in actionscript 2. The first raw version was created in 5 days, and then we worked on convenience, embodying completely crazy ideas 😃 For example, automatic attachment and rotation chemical bonds, breaking down elements into independent parts, and even own language markup for creating new elements.

Quick creation of chemical formulas

With a few collaborative ideas in the editor, you can create simple structures very quickly. For example, this picture was just created in 1 minute, and I did not draw from memory, but sketched:

Editor Features

• Objects can be immediately dragged to the "stage"
  (in other editors, you need to click on the object, and then click in the right place in the scene).
• To rotate an object, just point at it with the mouse and turn the mouse wheel (at the bottom, for control, the degree of rotation is indicated, the step is 3 °)
  (in other editors, either there are rotation buttons, and this is already a few unnecessary movements, or you can’t twist at all).
• Objects are attached to each other by edges or vertices (if you rotate the shape at the same time, it will rotate relative to the attached vertex)
  (no analogues).
• Simple text objects (C, CH, etc.) can be immediately taken and dragged to the desired location on the scene.
• Complex objects of type C 6 H 5 and chains are created simply - from a text string; then they can be moved, and they also cling to the vertices.

Pictures are optionally stored on the server. Pictures are saved static, so be careful when creating them - it will be impossible to edit them. On the other hand, it's not so scary, because you can draw the entire connection again in a matter of minutes, and at the same time fill your hand and train your head 😃 Just kidding 😃

Comments

interesting implementation

Alexander

Interesting thing, this editor
A good thing to quickly sketch chem. formula
(I found it by chance, tomorrow a friend of mine in chemistry should do
I'm not a chemist, but
There were 2 questions
1) How to adjust the size of elements?
(for example, the main thing is the font size)
2) Auto-positioning of elements into nodes seemed to me
"not too centered", ie. with some error
(relative to visual centers of letters)
which, upon closer examination, may disturb
picky teacher.
This is all, of course, a subjective opinion, but if there is
the question of finalizing the editor, I would recommend paying attention to the scalability of elements and the background grid
for ease of placement

1) The size of all elements is constant. If you need more or less, there is a solution: resize the browser window and make a printscreen. As for the font, for most formulas its relative size is optimal.
2) The positioning of the font elements really doesn't match their actual centers (or vertices). If this is very critical, then you will have to "finish" the final picture in Photoshop, for example.
In general, this editor is designed for simpler cases. For term papers, diplomas and any other printed works, it is better to use a full-fledged vector editor (I can’t advise something specific) or draw formulas in Word (but this, by the way, is not difficult :-).
The things you listed are from the category of prettiness, but it would really be nice to finish them. So far, we are collecting suggestions, comments, and when enough of them accumulate, we will start working on the next version of the editor.

Structural formula is a graphic representation chemical structure substances. It indicates the order of the atoms, as well as the relationship between the individual parts of the substance. In addition, the structural formulas of substances clearly demonstrate the valencies of all atoms included in the molecule.

Features of writing a structural formula

For compilation, you will need paper, a pen, the periodic system of elements of Mendeleev.

If you need to draw a graphical formula for ammonia, you need to take into account that hydrogen is able to form only one bond, since its valency is one. Nitrogen is in the fifth group ( main subgroup), has five valence electrons in its outer energy level.

Three of them he uses to form simple bonds with hydrogen atoms. As a result, the structural formula will be as follows: nitrogen is in the center, hydrogen atoms are located around it.

Instructions for writing formulas

In order for the structural formula to be written correctly for a particular chemical substance, it is important to have an idea about the structure of the atom, the valency of the elements.

It is with the help this concept it is possible to depict the graphic structure of organic and inorganic substances.

organic compounds

Organic chemistry involves the use of the graphic structure of chemicals of different classes when writing chemical reactions. The structural formula is compiled on the basis of Butlerov's theory of the structure of organic substances.

It includes four provisions, according to which the structural formulas of isomers are written, an assumption is made about the chemical properties of the analyte.

An example of compiling isomer structures

Isomers are called in organic chemistry substances that have the same qualitative and quantitative composition, but differ in the arrangement of atoms in the molecule (structure), chemical activity.

Questions relating to the compilation of the graphic structure of organic substances are included in the questions of a unified state exam held in 11th grade. For example, you need to compose, as well as give the name of the structural formulas of the isomers of the composition C 6 H 12. How to deal with such a task?

First you need to understand to which class of organic substances substances with such a composition can belong. Considering that two classes of hydrocarbons have the general formula C n H 2n at once: alkenes and cycloalkanes, it is necessary to compose the structures of all possible substances for each class.

To begin with, we can consider the formulas of all hydrocarbons belonging to the class of alkenes. They are characterized by the presence of one multiple (double) bond, which should be reflected in the preparation of the structural formula.

Considering that there are six carbon atoms in the molecule, we make up the main chain. We put a double bond after the first carbon. Using the first position of Butlerov's theory, for each carbon atom (valency four) we set the required amount of hydrogens. Naming the resulting substance, we use the systematic nomenclature, we get hexene-1.

We leave six carbon atoms in the main chain, move the position of the double bond after the second carbon, we get hexene-2. Continuing to move the multiple bond along the structure, we compose the formula of hexene-3.

Using the rules of systematic nomenclature, we get 2 methylpentene-1; 3 methylpentene-1; 4 methylpentene-1. Then we move the multiple bond after the second carbon in the main chain, and place the alkyl radical at the second, then at the third carbon atom, getting 2 methylpentene-2, 3 methylpentene-2.

Similarly, we continue to compose and name isomers. The considered structures represent two types of isomerism: carbon skeleton, multiple bond positions. It is not necessary to indicate all hydrogen atoms separately, you can use variants of abbreviated structural formulas, summing up the number of hydrogen for each carbon atom, indicating them with the corresponding indices.

Given that alkenes and cycloalkanes have a similar general formula, this fact must be taken into account when compiling the structures of isomers. You can first draw up the structure of a closed cyclohexane, then look at the possible side chain isomers, getting methylcyclopentane, dimethylcyclobutane, etc.

Line structures

Structural formulas of acids are typical representatives of this structure. It is assumed that each individual atom is indicated when creating their graphic formulas, indicating the number of valences between atoms by dashes.

Conclusion

According to ready-made structural formulas, it is possible to determine the valency of each element that is part of the substance, to suggest the possible chemical properties of the molecule.

After Butlerov's theory of the structure of organic substances was developed, it was possible to explain the difference in properties between substances that have the same qualitative and quantitative composition by the phenomenon of isomerism. Using the definition of valence, periodic system elements of Mendeleev, any inorganic and organic matter can be represented graphically. In organic chemistry, structural formulas are compiled in order to understand the algorithm of chemical transformations and explain their essence.

One of the most important tasks in chemistry is the correct compilation of chemical formulas. A chemical formula is a written representation of the composition of a chemical substance using the Latin designation of the element and indices. For the correct compilation of the formula, we will definitely need the periodic table and knowledge simple rules. They are quite simple and even children can remember them.

How to write chemical formulas

The main concept in the preparation of chemical formulas is "valence". Valency is the property of one element to hold a certain number of atoms in a compound. The valence of a chemical element can be viewed in the periodic table, and you also need to remember and be able to apply simple general rules.

• The valence of a metal is always equal to the group number, provided that it is in the main subgroup. For example, potassium has a valence of 1, and calcium has a valence of 2.
• Non-metals are a little more difficult. A non-metal can have a higher and a lower valency. The highest valency is equal to the group number. The lowest valency can be determined by subtracting the element's group number from eight. When combined with metals, non-metals always have a lower valence. Oxygen always has a valence of 2.
• In the combination of two non-metals, the lowest valency is that chemical element, which is located in the periodic table to the right and above. However, fluorine always has a valence of 1.
• One more thing important rule when placing coefficients! Total number The valencies of one element must always be equal to the total number of valences of another element!

Let's consolidate the knowledge gained on the example of a compound of lithium and nitrogen. The lithium metal has a valence of 1. The non-metal nitrogen is located in the 5th group and has a higher valence of 5 and a lower one of 3. As we already know, in compounds with metals, non-metals always have a lower valence, so nitrogen in this case will have a valency of three. We arrange the coefficients and get the desired formula: Li 3 N.

So, quite simply, we learned how to make chemical formulas! And for a better memorization of the algorithm for compiling formulas, we have prepared its graphical representation.