3.3 Organic Chemistry: .4 Alkenes Flashcards
what is the general formula of alkenes?
CnH2n
what are alkenes?
alkenes are unsaturated hydrocarbons
they contain a carbon to carbon double bond
give the name for each of these alkenes:
C2H4
C3H6
C4H8
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
C2H4= methene
C3H6= propene
C4H8= butene
C5H10= pentene
C6H12= hexene
C7H14= heptene
C8H16= octene
C9H18= nonene
C10H20= decene
what is the difference between but-2-ene and but-1-ene?
draw a diagram to show this
The position of the double bond (the functional group) is between the 2nd and 3rd carbons in the carbon chain
whlist the position of the double bond is between the 1st and 2nd carbons in the carbon chain
why cant nucleophiles be attracted to alkenes?
they dont have a polar bond
why are electrophiles attracted to alkenes?
because alkenes have a double bond which have high electron density
what is an electrophile?
an electron pair acceptor
describe what happens in electrophilic addition and why this process is called an addition mechanism?
- ) the electrophile is attracted to the double
- ) the electrons in the double bond make a coordinate bond with the electrophile and an intermediate is formed called a carbocation
- ) the nucleophile at the end will make a coordinate bond carbocation
- it’s addition because chemicals are added across the double bond
why hydrogen halides can be reacted with alkenes to form a halogenoalkane?
HCl, HBr and HI
draw out the electrophilic addition mechanism for the reaction between ethene and hydrogen bromide
draw the electrophilic addition mechanism for the reaction between ethene and concentrated sulphuric acid
state what product is made
what can you add to this product to produce an alcohol (what alcohol is made? )
- ethyl hydrogensulfate is made
- you can add water to the ethyl hydrogensulfate to produce ethanol as well as reforming the sulphuric acid
*first arrow should go directly to hydrogen and 3rd directly to carbon)
what is the test for an unsaturated hydrocarbon (alkene)?
explain why this happens
- orange bromine water
- you shake the alkene with orange bromine water, and the soltuion quickly decolourises (goes from orange to colourless)
- bromine is added across the carbon-carbon double bond to form a colourless dibromoalkane which happens by electrophilic addition.
draw out the electrophilic addition mechanism of the reaction between bromine and ethene
state the product that is made and the eqaution for the reaction
-the product made is 1,2-dibromoethane
(equation in image)
what will happen if a hydrogen halide is added to an unsymmetrical alkene?
there will be two possible products
what decides the amount of each product made from the reaction between a hydrogen halide and unsymmetrical alkene?
how stable the carbocation formed in the middle of the reaction is- which is known as the carbocation intermediate
what is carbocatio?
a carbocation is a carbon with a positive charge
what are the three types of carbocations?
primary
seconday
tertiary
what is the difference between the primary,secondary,tertiary carbocations?
- primary carbocations have 1 alkyl group attached to the C+ ion
- secondary carbocations have 2 alkyl groups attached to the C+ ion
- tertiary carbocations have 3 alkyl groups attached to the C+ ion
what is an alkyl group? give an example
alkyl groups are alkanes with a hydrogen removed
e.g methyl: CH3-
in the reaction between hydrogen bromide and propene:
- draw the 2 routes that the reaction could go through and write an eqaution for each
- state which is the major product and why
- state which is the minor product
2-bromopropane is the major product because this mechanism goes through the more stable secondary carbocation compared to the less stable primary carbocation making 1-bromopropane the minor product.
what is addition polymerisation?
the making of a long polymer from many alkene monomers
what happens in addition polymerisation?
- In addition polymerisation the monomers contain a double covalent bond
- the double bond breaks and the monomers add to each other to make a long chained molecule with single carbon-carbon covalent bond running through it
here is an alkene
show what this molecule would look like after being in a addition polymerisation reaction
what is another name for poly(phenylethene)?
polystyrene
why are polyalkene chains unreactive?
why is this causing problems?
- polyalkene chains are saturated molecules (they only contain single bonds in the carbon chain)
- the main carbon chain of a polyakene is non-polar
this means that the polyalkene chains cant not be attacked by biological agents e.g enzyme and so are not biodegradable, causing waste disposal to become more and more difficult
what are thermosoftening plastics?
- addition polymers consists of long polymer chains and the seperate chains are held together with weak Van der Waal forces
- These forces are easy to break so many addition polymers will melt in heating because the chains can slide over each other
how do plasticisers work?
- adding a plasticiser to a polymers makes it more flexible
- the plasticiser molecule gets between the polymer chains and push them appart
- this reduces the strenght of the intermolecular forces so they can slide around more, making the polymers easier to bend
what is the difference between rigid pvc and plasticised pvc (in terms of flexibility and uses
- rigid PVC is hard and brittle at room temperature so is used to make drainpipes adn window frames
- plasticised PVC is much more flexible than rigid PVC and is used to make electrical cable insulation, flooring tiles and clothing
what is the difference in properties between straight chain and branched chain polymers?
- )straight chain have a higher melting point than branched chained polymers:
- this is because in the straight chained polymer the chains lie closer together so the Van der Waal forces are stronger meaning more energy is required to overcome these forces.
- where as in branched chain polymers the chains lie further apart so the Van der Waal forces are weaker so less energy is required to overcome the forces - )Straight chained polymer has a higher density than branched chain polymers:
- this is because in the straight chained polymers there are more chains in a fixed volume
- where as with the branched chain polymer the chains are further apart and spread over a fixed volume
what are the solution to pollution by plastics?
- Mechanical recycling: this is seperating different plastics, washng them and sorting, melting and remoulding into new things
- Feedstock recycling: plastics are heated to a temperature that will break the polymer bonds and produce monomers. These can then be used to make new plastics. prob with this is that it cant be done a lot bc the heating can degrade the plastic’s properties
