Alkenes
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What is an alkene?
An unsaturated hydrocarbon.
What is a hydrocarbon?
A compound containing hydrogen and carbon atoms only.
What does unsaturated mean?
Contains one or more C=C double bonds.
What is the general formula of alkenes with one double bond?
CnH2n
How do you determine the root name of an alkene?
Find largest carbon change (eth-, prop- ect)
How should the carbon chain be numbered in alkenes?
So the double bond has the lowest possible number.
How is the position of the double bond shown in the name?
Number placed in the middle with dashes e.g pent-2-ene
How are branches or halogens shown in alkene names?
Numbered and added as prefixes in alphabetical order.
What is the priority order of functional groups (lowest to highest)?
Halogens –> Alkyl groups –> Alkenes –> Others
What intermolecular forces exist between alkene molecules?
Van der Waals forces only.
How do alkene physical properties compare to alkanes?
Very similar to equivalent alkanes.
How does melting/boiling point change with chain length?
Increases as chain length increases (stronger Van der Waals).
Are alkenes soluble in water?
No.
Why are alkenes more reactive than alkanes?
They are unsaturated and can undergo addition reactions.
Why are alkenes susceptible to electrophiles?
The C=C has high electron density (pi bond)
What type of combustion do alkenes undergo?
Combustion like hydrocarbons.
Why are alkenes rarely used as fuels?
Likely incomplete combustion so less energy and more CO or C formed.
Why are alkenes useful in synthesis?
They undergo many reactions and act as starting molecules.
What is the bond angle around a C=C double bond?
Planar with bond angles of around 120 degrees.
In larger alkenes which part is planar?
Only the C=C unit.
Can C=C bonds rotate?
No they are rigid.
What makes up a C=C double bond?
One sigma bond and one pi bond.
How is the sigma bond formed?
Overlap of 2s orbitals.
How is the pi bond formed?
Overlap of p orbitals and below the plane.