Alkenes Flashcards
What are alkenes?
Unsaturated hydrocarbons C=C bond
What is the general formula of alkenes?
CnH2n
How is a pi bond formed?
When electrons in the adjacent p orbital overlaps
What bond restrict the rotation of carbon atoms?
Pi bond
What is the angle and shape of a double bond?
Trigonal planar 120 degrees
Are alkenes more or less reactive than alkanes?
More reactive due to high electron density of double bond and pi bond is easier to break
What intermolecular forces of attraction do alkenes have?
London forces due to it not being polar
What is an electrophile?
Electron pair acceptors
What is the most stable carbocation intermediate?
A tertiary carbocation because it has the most alkyl groups attached, the most stable carbocation
Major products will be formed from which kind of carbocation?
Secondary or teriary
What conditions are needed for the electrophilic addition of H2O to an alkene?
Hydration reaction uses steam in the presence of an acid catalyst
What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?
Room temperature
Draw a mechanism for the reaction of HBr and ethene
…
How can an alkene be converted into an alkane?
- Alkene + Hydrogen = Alkane
- Hydrogenation, nickel catalyst 150 degrees
How do stereoisomerism arise?
The double bonds causes restriction and the groups attached to each carbon atom are therefore fixed.
What is the difference between cis-trans isomerism and E/Z isomerism?
For cis-trans one of the groups attached on each carbon atom of the double bond must be the same and for E/Z one of the groups attached on each carbon atom of the double bond must be different
What does E and Z stand for in stereoisomerism?
E = opposite side Z = the same side
What was Markownikoff’s rule?
The product with the most alkyl groups attached to it will be the major product (secondary or tertiary) and the product with the least alkyl groups attached will be the minor product (primary)
What carbocation is the most stable and why?
Tertiary carbocations has the most alkyl groups which means the positive charge of the carbocation is the most spread out, this makes the ion more stable.
What is an addition polymer?
Many monomers bonded together via rearrangement of bonds
What are monomers?
Single units that combine to form polymers. Usually have a C=C bond which breaks to leave a repeating unit.
What are the ways in which plastics can be disposed?
- Landfill
- Combustion
- Reuse/recycle
- Electricity generation
- Organic feedstock
What are the disadvantages of recycling?
- Plastics must be sorted
- Expensive
- Labour intensive
- Requires high technology
Why is PVC hazardous?
Due to its high chlorine content and when burnt it releases hydrogen chloride
Explain what happens in organic feedstock?
Plastics are separated and broken down into small organic molecules and then used to produce plastics
How does photodegradable polymers break down?
Polymers are weakened by absorbing light to start the degradation
How does biodegradable polymers break down?
Broken down by microorganisms into water, carbon dioxide and biological compounds
