Alkenes Flashcards
Why are alkenes vulnerable to attacks by electrophiles?
The double bond has a high electron density so species that want to gain electrons are attracted to it.
What are electrophiles?
electron pair acceptors
What is the name of the mechanism for the reaction of an alkene and a hydrogen halide to form a halogenoalkene?
electrophilic addition
Name and outline the mechanism for the reaction of ethene and hydrogen bromide.
Why can more than two different halogenoalkanes be formed if the alkene is unsymmetrical?
The halogen will be more likely to bind to the more stable carbonation because they have more alkyl groups that can distribute the charge on the carbon.
Name and outline the mechanism for the reaction of propene and hydrogen bromide. Draw the two products that could form in this reaction.
What is the name of the mechanism for the reaction of an alkene and a bromine to form a dibromoalkane?
electrophilic addition
Name and outline the mechanism for the reaction of ethene and bromine to form a dibromoalkane.
What is the name of the mechanism for the reaction of an alkene and sulfuric acid to form an alcohol?
electrophilic addition and hydrolysis
Name and outline the mechanism for the reaction of ethene and sulfuric acid to form an alcohol.
What is the test for unsaturation?
Add bromine water and if the solution decolorises then an alkene is present.
What do alkenes need to have for E-Z isomerism to arise?
- The restricted rotation around the double bond.
- Two groups are attached to each end of the double bond.
Why does but-1-ene not show E-Z isomerism?
Because on one side of the double bond, there are two identical groups.
What are polymers?
Large complex molecules made up of many monomers joined together.
What is addition polymerisation?
When many of the same monomers are bonded together by condensation reactions.
Why are addition polymers not very reactive?
They are non-polar.
Why do additional polymers with longer chains and little branches have higher melting and boiling points?
The bigger the chain is and the closer the molecules are to each other the stronger the van der Waals forces are so more energy is needed to break those forces.
What does PVC stand for?
Poly(chloroethene)
What is the repeating unit for PVC?
Why is PVC a hard material?
The chlorine atoms are more electronegative compared to the carbon and that means it has a slightly negative charge and the carbon has a positive one. This means that permanent dipole-dipole bonds can form between the PVC molecules. These forces need a lot of energy to break.
How do plasticisers make PVC softer?
They weaken the van der Waals forces between the PVC molecules by forcing them apart and that means less energy is needed to break those bonds and change the shape of the PVC
What is hard PVC used for?
drain pipes and window frames
What is soft PVC used for?
electrical cable insulation
