The diagram shows two types of reactions: decomposition and substitution. All of them proceed as radical. homolytic C-H splitting bonds proceed either under the action of heating (dehydrogenation), or under the action of radical particles formed from reagents (Br, Cl, NO2). Oxidation occurs only under severe conditions ( heat).
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 into two test tubes of 1 ml bromine water. 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, in which a mixture of sodium acetate and soda lime (a mixture of sodium hydroxide and calcium oxide) is placed, 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 homologous series 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. When chlorinating 2-methylpropane under conditions of radical substitution, 2 isomeric monochlorine derivatives are obtained. 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 structural formula hydrocarbon composition 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 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 the plane perpendicular to the plane arrangement of 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).
Chemical properties 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 also oxidizes easily. double bonds 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 are usually room temperature add bromine, forming colorless bromo derivatives, i.e. bromine water becomes decolorized.
Discoloration is just as easy. aqueous solution potassium permanganate. This is also a test for a double bond.
Heptane hardly enters into any reactions. This organic matter there are 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 free radicals. For example, in halogenation reactions, when 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 sulfochlorination reactions, 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 more low 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
In the absence of oxygen, the reaction can lead either to the formation carbon monoxide, it 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.
