Alkenes Flashcards
(24 cards)
General formula
CnH2n
Saturated or unsaturated?
Unsaturated - contain a C=C bond
What does the double bond consist of?
Sigma σ and Pi covalent bonds.
Which of the two bonds is stronger?
σ - sigma bonds are stronger than Pi bonds. The C=C is stronger than the C-C.
Which is longer?
C=C bond length is shorter than the C-C
How are σ bonds formed? And draw them
From the LINEAR overlap of 2 s-orbitals, an s-orbital and a p-orbital and two p-orbitals. All of which result in free rotation along the bond axis.
How are Pi bonds formed? and draw them.
The SIDEWAYS overlap of two p-orbitals, this results in restricted rotation along the bond axis.
What is the C=C bond a region of?
High electron density, which makes it open to attack from electrophiles.
What is more reactive alkanes or alkenes
Alkenes
What happens when alkenes undergo addition reactions?
The Pi bond is broken, the addition occurs across the double bond.
What are the conditions necessary for the complete combustion of an alkene?
A source of ignition and a plentiful supply of oxygen
Write an equation for the combustion of ethene
in book
What are the conditions for incomplete combustion?
A source of ignition and a limited supply of oxygen
Write an equation
in book
What is the name of the mechanism and draw the mechanism of the bromination of ethene.
Electrophilic addition - in book
Whats the splitting of HBr representative of?
Heterolytic fission
What do alkyl groups do to a carbocation?
They stabilise it, therefore a tertiary carbocation is more stable than a secondary carbocation which is more stable than a primary carbocation.
Does this affect the products made in any way
Yes, products that have a tertiary carbocation will be made much more than products which had a secondary etc.
What are the conditions and products for the hydrogenation of an alkene.
Conditions - finely divided nickel catalyst, 180ºC and 4atm
Product - an Alkane
What are the conditions and products for the hydration of an alkene with steam?
Concentrated phosphoric acid, 300ºC, 60-70atm
Ethanol
What are the conditions and products for the bromination of an alkene with bromine water?
Mix bromine water with liquid alkene or bubble the alkene through bromine water
A dibromoalkane
How do you test for a C=C bond?
If yellow bromine water changes to colourless the compound contains a C=C bond.
Draw the addition polymerisation 3 vinyl chloride molecules to form one polyvinyl chloride molecule via addition polymerisation
in book
What happens when you use excess reactant?
All the functional groups react
