ALKENE THEORY

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ALKENE THEORY
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Modelo del limoneno Alkenes are hydrocarbons that contain carbon-carbon double bonds. The word olefin is frequently used as a synonym.

Alkenes abound in nature. Ethene is a compound that controls plant growth, seed germination and fruit ripening.

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ALKENE THEORY
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Alkenes are named by replacing the -ane ending of the corresponding alkane with -ene. The simplest alkenes are ethene and propene, also called ethylene and propylene at the industrial level.

 
Rule 1.- The longest chain that contains the double bond is chosen as the main chain. Numbering begins at the end that gives the double bond the lowest locant.
 
alkenes nomenclature 1
 
[1] 1-Butene
[2] trans-2-Hexene
 
Rule 2.- The name of the substituents precedes that of the main chain and is accompanied by a locator that indicates its position in the molecule. The molecule is numbered so that the double bond takes the lowest locant.
 
alkenes 2 nomenclature
 
[3] 2-Propylhept-1-ene
[4] trans-4-Methyl-2-pentene

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ALKENE THEORY
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2-buteno: compuesto insaturado Each ring or cycle of a molecule implies the loss of two hydrogens with respect to an alkane of formula CnH2n+2 . The degree of unsaturation is the number of cycles and double bonds present in a molecule.

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ALKENE THEORY
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The following models show the structure, distances, and bond angles of ethene. Each of the carbons in the molecule is $sp^2$ hybridized. Its geometry is flat, with bond angles close to 120º.

alquenos-estructura-enlace

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ALKENE THEORY
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Alkenes have melting and boiling points close to the corresponding alkanes.

alquenos-propiedades-fisicas

Dipole moment in alkenes. In carbon $sp^2$ the electrons in the s orbital are closer to the nucleus and are strongly attracted to it, so that a carbon $sp^2$ has a tendency to attract electrons towards itself, which generates dipole moments.

alquenos-propiedades-fisicas

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ALKENE THEORY
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The heats released in the following hydrogenation reactions give us an idea about the different stability of alkenes.

stability alkenes 01
Increased stability

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ALKENE THEORY
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Alkenes can be prepared from haloalkanes and alkyl sulfonates by bimolecular elimination (E2). In the following example 2-bromo-2-methylbutane reacts with sodium methoxide to form a mixture of 2-methyl-2-butene and 2-methyl-1-butene.

sintesis-alquenos-e2

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ALKENE THEORY
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The treatment of alcohols with mineral acids at high temperatures causes the loss of water, which occurs through E1 or E2 mechanisms.

 
deshidratacion-alcoholes-01.png