Unsaturated hydrocarbons: alkenes, chemical properties and application

alkenes - unsaturated hydrocarbons whose molecules between two carbon atoms, one double bond.They are often called hydrocarbons ethylene series, since it is the simplest representative of ethylene HC2 = CH2.Sometimes called olefin hydrocarbons such as gaseous alkenes reacting with bromine or chlorine to form oily compounds that are not soluble in water.The word "alkenes" IUPAC is a derivative of the word "alkanes", in which the suffix -an replaced by the suffix -en, which indicates the presence in the molecule of the substance of the double bond.

Unsaturated hydrocarbons - alkenes: structure

All alkenes considered derivatives of ethylene or ethene - C2H4.

ethylene present in the molecule two carbon atoms and four hydrogen atoms, wherein the unsaturated carbon atoms.Each of the unsaturated carbon atom of a hybridized es and two pi orbitals, and one pi orbital remains in the "pure form" that ensures maximum distance hybridized electronic orbitals.Their axes form 120 °.This creates optimal condition

s for the overlap of electron orbitals.Three such orbital carbon atoms to form three sigma bonds (two C-H, C-C a).Consequently, the ethylene molecule has five sigma bonds that are localized in the same plane, forming between them an angle of 120 °.P-electrons, which have remained in the "pure" form another bond between two carbon atoms.Described the electronic structure of molecules of ethylene typical of alkenes.Unsaturated hydrocarbons must be considered as derivatives of ethylene.

to alkenes characteristic 2 type of isomerism - geometric and structural.

structural isomers of alkenes begins with butene C4H8.Distinguish and its variety - chain isomerism (or carbon skeleton), and isomers of the double bond placement in such a circuit.

geometrical isomers due to uneven placement hydrogen substituents in the molecule of ethylene relative to the plane of the double bond.Unsaturated hydrocarbons are cis and trans isomers.

alkenes in the free state is very rare in nature.They were synthesized using industrial and laboratory methods.

chemical properties of hydrocarbons: alkenes

They are caused by a double bond between two carbon atoms in the molecule of an alkene.

hydrogenation reaction

alkenes readily react with hydrogen addition.It takes place in the presence of catalysts or heat:

CH2 = CH2 = H2 H3C-CH3

Joining halides

reaction takes place on the Markovnikov's rule, that is, the interaction of hydrogen halides with asymmetric molecules alkenes hydrogen is added at the place of localization of the double bondpreferably to the carbon atom next to which there are more hydrogen atoms, a halogen atom - to the carbon atom next to which less hydrogen atoms or do not have them:

CH3-CH = CH2 + HC1-CH3-CH3-CHC1.

Application hydrocarbons

Eten - gas is readily soluble in alcohol and bad water, explosive.They are rich

cracking gases (up to 20% of total weight) and coke oven gas (approximately 5%).In the laboratory methods of dehydration of ethylene prepared dehydrogenation of ethane and ethanol.Applied to obtain ethylene ethyl alcohol, vinyl chloride, ethylbenzyl, polyethylene, antifreeze agents (substances which reduce the freezing point of water in engines) and other organic substances.In human and veterinary medicine, ethylene is used as a narcotic drug, in plant breeding - to speed up the ripening of fruits (tomatoes, lemons, etc.).

Propylene is obtained with the ethylene in the pyrolysis and cracking of various types of petroleum feedstocks.Propylene - a motor fuel component.It is used as feedstock for polypropylene izopropilbenzena isopropyl alcohol.With isopropanol, acetone, with izopropilbenzena - acetone and phenol.Propylene is used as a narcotic drug for synthesizing acrylonitrile, cumene, butanol, etc.