Olefins - hydrocarbon molecule which has one double bond.Sometimes the present compounds called hydrocarbons ethylene series.The double bond in the molecule is easily identified by spectral analysis.
The physical properties of alkenes
first three members of the homologous series of alkenes - gases.From the fifth to sixteenth - liquid, high molecular weight alkenes - solids.With increasing length of the hydrocarbon chain increases and the boiling point substances.In laboratory conditions, these substances can be obtained in several ways: by the dehydrogenation of alkenes, petroleum cracking, dehydrogenation of alcohols.
oil cracking - industrial method of producing unsaturated hydrocarbons.As a result of the thermal cracking of oil heated to 750 degrees, alkane hydrocarbon skeleton is broken:
S30N62 → S15N30 + S15N32
dehydrogenation of alkanes .This process is carried out at a temperature of about 600 degrees.Under these conditions, the saturated hydrocarbon molecule of H atoms are cleaved to form alkenes, for example: → S5N12 S5N10 + H2.
alcohol dehydration .Monohydric alcohols interacts with sulfate acid to form alkenes, for example S4N9ON → C4H8 + H2O.
alkenes chemical properties linked to the presence in their molecule a double bond.The electron density between the C-atoms connected by a double bond is higher than that between the C-atoms connected by single bonds.The main type of reaction, which come into alkenes - attaching accompanied rupture pi bond to form two new sigma bonds.The olefins react polymerization, which is also accompanied by cleavage of double bonds.
Chemical properties of alkenes: joining halides
Olefins easily attached to a molecule of hydrogen halides themselves, forming monogalogenoproizvodnye (eg S10N20 + HC1 → S10N21S1).Upon accession of H2O to alkenes formed saturated monohydric alcohols (S10N20 + N2O → S10N21ON).
Burning alkenes
at high temperatures under the influence of O2 olefins are easily oxidized (burned) to H20 and C02.Alkenes, interacting with potassium permanganate to form a dihydric alcohols (glycols).
Chemical properties of alkenes: polymerization of olefins
presented hydrocarbons are more inclined to the polymerization reaction.Typically, the polymer - with a long chain of repeating structural units (monomers).This process may be triggered in several ways, but in most cases it is a chain, and relates to a free radical, cationic or anionic processes.
Chemical properties of alkenes: cationic polymerization
This type of reaction is catalyzed by acid.Proton joins the olefin forming a carbocation.This is followed by an attack on the last pi sitemu another molecule and forms alkene carbocation longer chain that attacks following olefin molecule, etc.As a result, the ejection of a proton or any other process, the "quenching" charge carbocation, an open circuit occurs.When anionic polymerization is started anion formed by nucleophilic attack of the anion X- olefin.When you join a proton chain breaks.Note that polymerizes via a free radical mechanism, most of the unsaturated hydrocarbons.This process may be initiated H202, organic peroxides, hydroperoxides, etc.Open circuit is due to the recombination of radicals.In some cases, for the preparation of polymers of alkenes used copolymerization reaction.In the copolymerization, a polymer comprising various parts, alternating in the macromolecule in a certain way.The reaction produces the product copolymer.Physical and mechanical properties of the present compounds are determined primarily by the order of the alternation of elementary units, and the type and quantity of monomers incorporated into the polymer chain.
