Alkenes Flashcards
What is a C=C double bond?
An area of high electron density
Why are alkenes highly reactive?
Their C=C double bond
How is the C=C double bond formed?
The overlap of a spare unbonded singly filled p-orbital present on each carbon atom in the bond
Can a C=C double bond be rotated?
NOPE
What is the general formula for alkenes?
Cn H2n
What is the bond angle and shape name for the C=C double bond in alkenes?
120
Planar
When naming alkenes what must you always check for?
E/Z isomerism
What is the only mechanism in the alkenes topic?
Electrophilic addition
Are alkenes or alkanes more reactive?
Alkenes
What is an electrophile?
A species that Accepts a pair of electrons
What area of alkenes is easily attacked by electrophiles?
Why?
The C=C double bond
It has a high electron density
Describe the mechanism to turn alkenes to alkanes briefly
Give this mechanism’s name
An electron pair is donated to the electrophile which causes C=C double bond to break, allowing each C to form bonds with other species
Electrophilic addition
Describe the electrophilic addition mechanism with the electrophile X-Y
1) an e- pair from the C=C bond forms a covalent bond with the delta positive X, breaking the X-Y bond and forming a :Y- ion. An intermediate with a *ve carbocation is formed
2) lone pair on :Y- forms a covalent bond with +ve carbon
In electrophilic addition with Bromine water, what does the :Br- ion act as?
A nucleophile
Bromine water is non-polar. How does electrophilic addition occur?
Electron rich double bond induces a dipole and delta positive Br acts as the electrophile
In a H-X molecule, where X is a halogen atom, which is delta positive?
The H is delta positive
How to write sulphuric acid for electrophilic addition
H-OSO3H
What is hydrolysis?
Splitting a molecule with water or another small molecule
What does the addition of ethyl hydrogen sulphate to water cause and produce?
What is the overall equation?
What does H2SO4 act as? Why?
Hydrolysis
Ethanol
CH2=CH2 +H2O —-> CH3CH2OH
A catalyst. It is not used up?
What is the most stable carbocation?
The least stable?
Tertiary
Primary
What is the major product formed from?
The more stable carbocation
How do you determine the class of the carbocation?
The number of carbon atoms directly bonded to the positively charged carbon atom
What is the stability of carbocations related to?
Why?
The presence of alkyl groups (CH3, CH2, CH)
Electron releasing relative to the hydrogen atoms and help to stabilise the positive charge on the carbocation
What is the electron releasing property of alkyl groups called?
Positive inductive effect
Will asymmetrical alkenes form equal amounts of each product?
No. The more stable carbocation intermediary will form more products than the less stable one
What is the mechanism to form a polymer ?
Addition polymerisation
What is the repeating unit for poly (ethene)?
H. H
|. |
-(-C-C-)-
|. |
H. HGive the IUPAC name for PVC?
poly(chloroethene)
Describe normal PVC
Hard and rigid as there are permanent dipole-dipole forces between chains due to delta positive C and delta negative Cl
Why are plasticisers added?
To reduce the effectiveness of the dipole dipole forces between PVC chains and make the plastic more flexible
The more plasticiser you add…
The more flexible the plastic becomes
What is the most common plasticiser?
Phthalates
Give 3 uses of normal PVC
Doors
Windows
Guttering
Give uses of plasticised PVC
Cable insulation
Imitation leather
Inflatable products
What are the problems with plastics?
Non-biodegradable due to strong covalent bonds so buried plastics could take hundreds of years to decompose
How are plastics broken down?
Heated or remoulded by heating so Van der Waals’ are broken
What happens to poly(ethene)?
Poly(propene)?
It is separated from others, washed, melted, and remoulded
Heated to high temp to break polymer bonds and produce monomers which can be used to make new plastics
Typical uses of
Poly(ethene)
Poly(propene)
Plastic bags, washing up bowls
Rope
