Physical Properties, IUPAC Nomenclature and Isomers of Alkene

Alkene is a hydrocarbon compound and there is at least one double bonds between two carbon atoms. Alkenes are introduced as olefin. Due to existence of double bonds, alkene are considered as unsaturated hydrocarbons and physical and chemical properties are heavily affected due to that. But, in this tutorial, we only focus physical properties of alkene and chemical properties of alkenes are discussed in a separate tutorial.

Content

• Physical properties of alkenes
• IUPAC Nomenclature of alkenes
• Isomers of alkenes
  • Steps of drawing isomers
  • How physical properties vary with each isomer

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Physical properties of alkenes

Under physical properties, we will see physical status at room temperature, meting and boiling points of alkene.

Physical states of alkenes at room temperature

Physical state of the alkene compound at room temperature depend on the strength of intermolecular forces and molecular mass of respective alkene as other compounds.

• Ethene, Propene, n-butene which are simplest alkene compounds are gases.
• Alkenes containing carbon atoms 5 to 18 are liquids.
• More than 18 carbon atoms in alkenes are solids.

Melting and Boiling points of alkenes

Alkenes have higher melting and boiling points than the corresponding alkanes because alkenes have a pi ( Π ) bond in it's double bond. Pi ( Π ) bonds are more polarizable than sigma (σ) bonds. Therefore intermolecular forces between alkene molecules are more stronger than between alkane molecules.

As other compound series, boiling and melting points are increased with molecular mass.

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IUPAC Nomenclature of alkenes

We can give a IUPAC name to every alkene compound. Usually IUPAC nomenclature of an alkene compound ends with "ene" suffix such as "ethene, "propene and etc. Because alkene compounds are simple in structure, it is not difficult to naming alkenes.

How to name when there are two or more double bonds in an alkene compound

There may be two or more double bonds in some alkene compounds.

Isomerism of alkenes

Geometrical isomerism is the important isomerism case we study in alkenes due to double bond of alkenes. Other isomerism cases such as optical, chain and position isomerism cases also may be exist.

General formula of alkenes

C_nH_2n [n=2,3,4....]

Ex: if n=3;
Respective hydrocarbon : C₃H_2*3 = C₃H₆

What is the simplest alkene

Simplest alkene contains only two carbon atoms. According to the general formula of alkene, number of hydrogen atoms are four in the simplest alkene. Therefore ethene( C₂H₄ ) is the simplest alkene.

Structural isomers of alkenes

Chain and position isomers are demonstrated by alkenes as structural isomers.

Structural isomers of butene

Geometrical isomerism of 2-butene

There are two geometrical isomerism in 2-butene.

Geometrical isomerism of C₅H₁₀

Geometrical isomerism structures for are figured below.

Study the figure. You can see the number 2 carbon in the molecule A has two different groups as -CH₃ and -H. If we interchange that two groups we get a new compound. Physical and chemical properties of A and B are different. A structure is cis isomerism and B is trans isomerism.

Hybridization of alkenes

Hybridization of ethene

Ethene only has two carbon atoms which are bonded by a double bond. Each carbon atom has three hydrogen atoms. When consider one carbon atom, it has three σ bonds and one Π bond. Therefore hybridization of that carbon ato is sp³.

Hybridization of propene

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