Alkenes Flashcards
What are alkenes?
Unsaturated hydrocarbons that contain at least 1 c=c bond made up of a π bond and a σ bond
What is the general formula of alkenes?
CnH2n
How is a π bond formed?
Electrons in the adjacent p orbital overlap above and below the carbon atoms. They can only be made after a σ bond formed.
What bond restricts the rotation of carbon atoms?
π bond
What is the angle and shape of a double bond?
Trigonal planar
120 degrees
Are alkenes more or less reactive than alkanes? Why?
More reactive due to high electron density of double bond and the fact that the π-bond is slightly easier to break.
What intermolecular forces of attraction do they have?
Only london forces due to non-polar bonds.
Are they soluble in water? Why?
No. Non-polar bonds
Write an equation for the complete combustion of pent-2-ene
CH3CH=CHCH2CH3 + 7 1/2 O2 —> 5CO2 + 5H2O
What are the types of isomers that can be formed using alkenes?
E/Z isomers - due to the restricted rotation
Cis-trans isomers - if two of the same substituents are attached to each carbon.
What is an electrophile?
Species that are electron pair acceptors
What is the most stable type of carbocation intermediate? Why?
Alkyl groups have a positive inductive effect, so the most stable carbocation is the one bonded to the most other carbon atoms.
Major products will be formed from which kinds of carbocations?
Tertiary ( or the most stable available )
What conditions are needed for the electrophilic addition of H2O to an alkene? What is this type of reaction called?
Steam in the presence of an acid catalyst, usually phosphoric acid.
Reaction is called hydration
What are the products of the hydration reaction?
An alcohol
What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?
Hydrogen halide gases must be at room temperature
What is the reaction called when a halogen is added to an alkene?
Halogenation
How can an alkene be converted into an alkane? What is the reaction called and what are the required conditions?
Alkene + hydrogen = alkane
Hydrogenation
Conditions —> 150 degrees, nickel catalyst
What is an addition polymer?
Many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule
What are monomers? What form do they usually take?
Molecules which combine to form a polymer
Usually have a c=c bond which breaks to leave a repeating pattern
What are the ways in which plastics can be disposed?
- Landfill
- Combustion
- Electricity generation
- Reuse
- Recycle
- Organic feedstock
What are the disadvantages of recycling?
- plastics must be sorted into different types
- expensive
- labour intensive
- requires high technology
How does photodegradable polymers break down?
They are broken down chemically using energy with wavelengths similar to light. Once the break down begins it is not possible to stop the process.
Explain what happens in organic feedstock.
Plastics are separated and broken down into small organic molecules through a series of reaction. The molecules can then be used to produce plastics and in other industries
Give a disadvantage of photodegradable polymers.
May not be exposed to sufficient light.
