Chemical properties of alkanes. Heptane Isomers: General Characteristics and Applications Physical and Chemical Properties

The diagram shows two types of reactions: decomposition and substitution. All of them proceed as radical. Homolytic cleavage of C-H bonds proceeds either under the action of heating (dehydrogenation), or under the action of radical particles formed from reagents (Br, Cl, NO2). Oxidation occurs only under harsh conditions (high temperature).

An example of a radical substitution reaction mechanism:

During bromination and nitration according to Konovalov, predominantly secondary and tertiary alkyl halides and nitro-substituted ones are formed, since secondary radicals are more stable than primary ones.

LAB #1

Experience 1. Burning alkanes.

Put 2 ml of heptane and 0.5 g of paraffin into porcelain cups, set fire. (Experiment performed under draft). Follow the nature of the flame. Write the equations for the combustion of heptane and paraffin. Record your observations and conclusions in a journal.

Experience 2.Interaction of alkanes with bromine.

Pour 1 ml of bromine water into two test tubes. Add 1 ml of n-heptane to one tube and 1 ml of cyclohexane to the other. Shake the contents of the tubes. Record observations and conclusions in a laboratory journal.

Experience 3.Interaction of alkanes with a solution of potassium permanganate.

Pour 1 ml of potassium permanganate solution into two test tubes. Add 1 ml of heptane to the first tube and 1 ml of cyclohexane to the second. Shake the tubes. Record observations and conclusions in a laboratory journal.

Experience 4.Getting methane.

Heat a test tube with a gas outlet tube containing a mixture of sodium acetate and soda lime (a mixture of sodium hydroxide and calcium oxide) in a burner flame until gas begins to evolve. (To see gas evolution, lower the gas tube into a test tube with 2 ml of water). Light up the gas. Prove that the evolved gas is an alkane (Experiments 2 and 3).

The reaction equation for the formation of methane from sodium acetate.

Tasks (alkanes)

1. What is the general formula for the homologous series of alkanes? Write the structural formulas and name the isomers of the composition: C 4 H 10, C 5 H 12, C 6 H 14. Indicate in these formulas the primary, secondary, tertiary and quaternary carbon atoms.

2. Write the structural formulas of heptane isomers containing tertiary and quaternary carbon atoms and name them.

3. Name the following hydrocarbons according to the IUPAC nomenclature:

4. With which of the following compounds does n-butane react under the indicated conditions? 1) HNO 3 (razb.) / t °, r; 2) H 2 SO 4 (conc.)/20°C; 3) O 2 (flame); 4) KMnO 4 /H 2 O, 20°C; 5) SO 2 +Cl 2 /hn; 6) HNO 3 (conc.)/20°С; 7) Br 2 /hn, 20°C; 8) Br 2 /20°C (in the dark). Write the equations for these reactions.

5. What monochloro derivatives are formed during chlorination of: a) propane, b) 2-methylbutane, c) 2,2-dimethylpropane? What are the reaction conditions? What is the reaction mechanism?

6. Chlorination of 2-methylpropane under radical substitution conditions yields 2 isomeric monochloro derivatives. What is their structure, and which one is easier to form? What are the reaction conditions?

7. Write the Konovalov nitration reaction (10% HNO 3 , 140°С, pressure) for the following hydrocarbons: ethane, propane, 2-methylbutane. Name the reaction products. Which one will form the easiest? Specify the reaction mechanism.

8. Write the structural formula of the composition hydrocarbon C 5 H 12, if only the tertiary bromine derivative is obtained during its bromination.

9. Write the reaction mechanism of photochemical sulfochlorination of n-hexane. What is SMS? What properties are based on their use?

10. Get ethane by all methods known to you, define the s-bond. What are its main differences from ionic bonding?

ALKENES

Alkenes are hydrocarbons that have double bonds between carbon atoms. They have the general formula C n H 2 n. The carbon atoms at the double bond are in a state of sp 2 hybridization.

Three hybrid sp 2 orbitals of such a carbon atom are located in a plane; the angle between them is 120°. An unhybridized p-orbital is located perpendicular to this plane.

Molecule model of ethene (ethylene) CH 2 = CH 2

One of the multiple bonds formed by overlapping hybrid orbitals is called an s-bond. The other bond formed by the lateral overlap of the p z orbitals is called the p bond. It is less strong than the s-bond. The p-bond electrons are more mobile than the s-bond electrons. In alkenes, the p-bond is located in a plane perpendicular to the plane of the s-bonds.

For ethylene hydrocarbons, two types of isomerism are possible: structural (chain isomerism and multiple bond position isomerism) and geometric ( cis-trance) isomerism. Geometric isomerism is due to the different arrangement of substituents relative to the plane of the double bond.

At cis-isomers, the substituents are located on one side of the plane of the double bond, in trance-isomers are amazing. Trance-isomers are thermodynamically more stable than cis-, since they lack steric (spatial interaction between substituents).

Methods for obtaining alkenes are based on the elimination of hydrogen, halogens, water or hydrogen halides under the action of heating or appropriate reagents (NaOH/alcohol, H 2 SO 4 , t°C).

The chemical properties of alkenes are associated with the presence of a p-bond in them, which easily transforms into more stable s-bonds, i.e. enters into an addition reaction.

It is also easy to oxidize double bonds with an aqueous solution of potassium permanganate.

These reactions are called electrophilic addition reactions and proceed in two stages.

Addition to unsymmetrical alkenes occurs according to Markovnikov's rule. The predominant formation of secondary and tertiary derivatives is due to the fact that the most stable tertiary or secondary cation is formed intermediately.

Alkenes are identified by their ability to undergo addition reactions. Alkenes usually add bromine at room temperature, forming colorless bromo derivatives, i.e. bromine water becomes decolorized.

Discoloration of an aqueous solution of potassium permanganate occurs just as easily. This is also a test for a double bond.

Heptane(from other Greek ἑπτά - seven) CH 3 (CH 2) 5 CH 3 - an organic compound of the alkane class. Heptane and its isomers are colorless liquids, readily soluble in most organic solvents, insoluble in water. They have all the chemical properties of alkanes.

Physical and chemical properties

Colorless flammable liquid with a flash point of minus 4°C, an autoignition temperature of 223°C. The area of ​​ignition of heptane vapor in air is 1.1-6.7% (by volume).

Similar to the chemical properties of other higher alkanes.

Safety

Reference normal heptane is a hydrocarbon of the paraffin series, has a narcotic irritant effect. Prolonged exposure to heptane causes mild skin irritation and indigestion.

The maximum permissible concentration of heptane vapors in the air of industrial premises (in terms of carbon) is 300 mg/m 3 .

The concentration of heptane vapor is determined by the linear color method using a universal gas analyzer.

Equipment and communications must be sealed, the premises must be equipped with proper ventilation. During work related to the production of normal heptane, personnel should undergo a medical examination once every 12 months.

As personal protective equipment, a grade A filter gas mask, special clothing, special footwear and safety devices are used in accordance with the current standard industry standards.

In case of fire of standard normal heptane, the following fire extinguishing agents should be used: sand, chemical foam, water mist, inert gas, asbestos blanket, powder and gas fire extinguishers.

Heptane hardly enters into any reactions. This organic substance has nine (and if we also count optical ones, then 11 isomers can be distinguished). All of them have the same empirical formula C7H16, but differ in structure and, accordingly, in physical properties.

All isomers are colorless, transparent, flammable liquids with a pungent odor. Their boiling point ranges from 79.20°C (2.2-dimethylpentane) to 98.43°C (n-heptane). And the density ranges from 0.6727 grams / cm3 (2,4-Dimethylpentane) to 0.6982 grams / cm3 (3-Ethylpentane).

Heptane isomers are practically insoluble in water, but readily soluble in many organic liquids. They are inactive, but they can participate in reactions that occur with the formation of free radicals. For example, in halogenation reactions, at elevated temperature or UV irradiation. However, in this way it is possible to carry out fluorination, chlorination or bromination, and iodine does not react with these substances.

It is known that they can also participate in the reactions of sulfochlorination, catalytic oxidation. They are able to decompose (this requires either a very high temperature, over 1000 ° C, or the presence of a special catalyst, which allows the reaction to be carried out at lower temperatures, about 400 - 500 ° C), as well as burn in an oxygen atmosphere, with the formation of water and carbon dioxide. This reaction proceeds according to the following formula: 2 С7Н14 + 21О2 = 14СО2 + 14Н2О

With a lack of oxygen, the reaction can either lead to the formation of carbon monoxide, the formula will look like this: С7Н14 + 7О2 = 7СО + 7Н2О.

Or to the formation of carbon. In this case, it can be written as a reaction: 2С7Н14 + 7О2 = 14С + 14Н2О

How isomers of heptane are used

N-heptane serves as a raw material for the production of certain types of organic compounds. In addition, it is used as a primary standard in determining the detonation properties of fuel, since its octane number (an indicator characterizing the ability of a fuel to resist self-ignition during compression) is 0. And one of the isomers of this organic substance, 2,2,3-Trimethylbutane, on the contrary, increases the octane number of fuel, and therefore is widely used as an additive to it.