alkenes Flashcards
Define alkenes
Unsaturated hydrocarbons that contain at least a C=C bond are made up of a pi bond and a sigma bond
What is the general formula of alkenes
CnH2n
How is a pi bond formed
Electrons in the adjacent p orbitals overlap above and below the carbon atoms, they can only be made after a sigma bond is formed
What bond restricts the rotation of carbon atoms
pi bond
What is the angle and shape of a double bond
Trigonal planar
120
Are they more or less reactive than alkanes? Why?
More reactive due to the high electron density of double bond and the fact the pi-bond is slightly easier to break
What intermolecular forces of attraction do alkenes have?
Only London forces due to non-polar bonds
Are they soluble in water? Why?
No, non-polar bonds
What are the types of isomers that can be formed using alkenes?
E/Z isomers - due to the restricted rotation
Cis-trans - 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 carbonation intermediate? Why?
Alkyl groups have a positive inductive effect, so the most stable carbonation is the one bonded to the most other carbon atoms
Major products will be formed from which kinds of carbocations
Tertiary (or most stable available)
What conditions are needed for the electrophilic addition of H2O to an alkene? What is the type of reaction called?
Steam in the presence of acid catalyst - phosphoric acid
The reaction is called hydration
What are the products of an alkenes hydration reaction
An alcohol
What are the conditions 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 alkene?
Halogenation
How does a molecule with a non-polar bond react as if its an electrophile?
C=C double bond with a high electron density induces a temporary dipole in the halogen molecule
How can an alkene be converted into alkane? What is the reaction called and what are the required conditions?
Alkene + hydrogen = alkane
hydrogenation
conditions: 150C, nickel catalyst
What is an additional 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 of?
- Landfill
- Combustion
- Electricity generation
- Reuse
- Recycle
- Organic feedstock
What are the disadvantages of recycling
- Plastic must be sorted into different types
- Expensive
- Labour intensive
- Requires high technology
How do photodegradable polymers break down
They are broken down chemically using energy with wavelengths similar to light
Explain what happens in organic feedstock
Plastics are separated and broken down into small organic molecules through a series of reactions, the molecules can be used to produce plastic and in other industries
Give a disadvantage of photodegradable polymer
May not be exposed to sufficient light
