3.3.4 Alkenes Flashcards
What are alkenes?
Unsaturated hydrocarbons.
What is the general formula for an alkene?
CnH2n
What shape is ethene and what are its bond angles?
Planar, 120 degrees.
What are electrophiles?
+ ions or electron deficient atoms and act as e- pair acceptors.
What does being an e- pair acceptor mean?
They seek e- rich sites.
What state does HBr react with alkenes and what does it form?
Gas or concentrated aqueous solutions, to form bromoalkenes.
Ethene + HBr ->
1-bromoethane
What conditions in the HBr molecule make it suitable to react in an electrophillic addition reaction?
Br is > electroneg than H, makes HBr polar.
What happens in the electrophilic addition reaction between H in the HBr and the C = C bond?
Electrons from the double bond move, forming a new C-H bond.
What happens to the e-s in a electrophilic addition in the H-Br bond?
E-s shift towards Br making a bromide ion (tow dots Br -).
What happens to the C = C bond in electrophilic addition with HBr?
Breaks, leaving a C to become an e- deficient carbocation.
What is a carbocation?
Species which contains a carbon atom that has a+ charge.
What does the Br- ion do in electrophilic substitution?
Acts as a nucleophile, attacks the carbocation, using its lone pairs to form a new bond between C and Br.
Under what conditions do an alkene and sulphuric acid react, what does this form?
Alkene reacts with a cold, conc. sulphuric acid. Forms alkyl hydrogensulphates.
What do two p orbitals produce when they overlap?
Pi orbitals.
What can alkyl hydrogen sulphates be hydrolysed to, under what conditions?
Hydrolysed to an alcohol by reacting it with warm sulphuric acid.
What is bromine water the test for, how does it change?
Alkenes, red/brown to colourless.
Why don’t we use bromine water to test for alkanes?
Don’t react.
If the alkene and the electrophile being added are both unsymmetrical what two possible products are formed?
Major and minor product.
What is the major product formed by?
The more stable carbocation.
What is the order of stability of the carbocations?
Tertiary > Secondary > Primary.
Why does more alkyl groups around the carbocation do and what is more likely to happen?
Make it more stable, more likely to be formed.
What is a tertiary carbocation bonded to?
3 C / 0 H.
What is a secondary carbocation bonded to?
2 C / 1 H.
What is a primary carbocation bonded to?
1 C / 1 H.
Why can’t you produce major and minor products from a reaction with Br2?
Br2 is symmetrical.
Explain the circumstances needed for a major and minor product to be formed in roughly equal amounts.
Both the same level of carbocation, electrophilic addition can occur on either carbon, no preference between the two.
Can you draw the structure out when a question asks you for a balanced equation?
Yes.
When identifying a product do you need to name it?
No you can just draw it instead.
What are polymers formed from?
Monomers.
What are monomers?
Tiny repeating units.
What are polymers formed in the presence of?
A catalyst.
How are polymers represented?
Using a repeating unit.
What makes polyalkenes unreactive?
They are saturated.
What are the strong bonds in a polyalkene?
C-H and C-C.
Do polyalkenes biodegrade?
No, not attacked by biological agents (enzymes).
What are plasticisers, what are they used for and why?
Small molecules that fill the gaps between the polymer chains, added to a polymer to modify them so chains can slide over eachother.
Give an example of how a plastic changes with use of a plasticiser.
PVC, drainpipes and aprons.
How are polymers written from the monomer?
A long C chain with whatever is attached to the monomer.
How is a repeating unit written?
One part of the polymer is put in square brackets, the bonds on either side must go out of the brackets.
What is the everyday name for polyethene and what is it used for?
Polythene, used for making plastic bags, packing film, squeezy bottles.
What is the everyday name for polypropene and what is it used for?
Polypropylene, used for making ropes, plastic chairs and carpet.
What is the everyday name of phenylethene?
Polystyrene.
What is the everyday name of chloroethene?
PVC.
What is the everyday name of tetrafluoroethene?
PTFE / Teflon.
What is the everyday name of methyl 2-methylpropenoate?
PMMA, Perspex.
