4.1.3 Alkenes Flashcards
(25 cards)
What are alkenes?
Unsaturated hydrocarbons that contain at least one C = C bond made up of a pi bond and a sigma bond
What is the general formula for alkenes?
CnH2n
How is a pi π bond formed?
Electrons in the adjacent p orbitals overlap above and below the carbon atoms they can only be made after the σ bond is formed
What bond restricts the rotation of carbon atoms?
πbond
What is the angle and shape of a double bond
Trigonal planer
120 degrees
Are alkenes more or less reactive than alkanes?
More reactive due to high electron density of double bond and the fact the pi-bond is slightly easier to break
What intermolecular force do alkenes have?
On,y London forces due to non polar bonds
Are alkenes solvable in water?
No, non polar bonds
What are the types of isomers that can be formed using alkenes?
E/Z isomers - due to restricted rotation
Cis-trans isomers - if two of the same substituents are attracted to each carbon
What is an electrophile?
Species that are electron pair acceptors
What is the most stable type of carbocation intermediate?
Alkyl groups have a positive inductive effect, so the most stable carbocation is the one bonded to the most other carbon atoms ie. Tertiary carbocation
Major products will be formed from which kinds of carbocation?
Tertiary (or the most stable)
What conditions are needed for electrophilic addition of H2O to an alkene? What is the 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 alkene?
Halogenation
How does a molecule with a non polar bond react as if it is an electrophile?
C=C double bond with a high electron density includes a temporary dipole in the halogen molecule
δ+ atom attracted to double bond
How can an alkene be converted to 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 and what form do they usually take?
Molecules which combine to form a polymer
Usually have C=C bonds 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 do 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 produce plastics and in other industries
