Alkenes Flashcards
What are alkenes?
Unsaturated hydrocarbons
What is an unsaturated hydrocarbons?
One which contains at least one carbon-carbon double bond
What electrophiles can alkenes undergo addition reactions with?
HBr, Br2 and H2SO4
What is the mechanism for the electrophilic addition of HBr to an alkene?
Electrons go from the C=C double bond to the δ+ H and the electrons from the H-Br bond go to the Br. Then the lone pair on the Br- goes to the positive C of the carbocation intermediate
What is the mechanism for the electrophilic addition of Br2 to an alkene?
Electrons go from the C=C bond to the δ+ Br and the electrons from the Br-Br bond go to the δ- Br. Then the lone pair on the Br- goes to the positive C of the carbocation intermediate
What is the mechanism for the electrophilic addition of H2SO4 to an alkene?
Electrons go from the C=C double bond to one of the δ+ Hs and the electrons from that O-H bond go to the O. Then the lone pair on that O go to the positive C of the carbocation intermediate
What is a carbocation?
A species with a positive charge on a carbon atom
How are carbocations classified?
As primary, secondary or tertiary depending on the number of alkyl groups (-R) attached
Which carbocations are the most and least stable?
Tertiary carbocations are the most stable and primary carbocations are the least
What is the major product of a reaction?
The product that is produced in larger quantities due to the relative stability of the carbocations formed
What is bromine water used to test for?
Unsaturation
What will be observed if bromine water is added to an alkene?
It will turn colourless
What will be observed if bromine water is added to an alkane?
It will remain orange
What are addition polymers produced from?
Alkenes
How are addition polymers produced from alkenes?
The double bond is broken to form a repeating unit
Why are addition polymers unreactive?
They don’t have a double bond
How is addition polymers being unreactive a good thing?
They can be used for everyday plastic products
How is addition polymers being unreactive a bad thing?
They’re not biodegradable
What is the natural state of PVC?
Rigid
What happens to PVC when a plasticiser is added to it?
It becomes flexible
What is rigid PVC used for?
Window/door frames and drainpipes
What is flexible PVC used for?
Wellington boots and raincoats
Why do polymers have high boiling points?
The individual molecules contain strong covalent bonds and there are van der Waal’s forces between the molecules which are strong because of the molecule’s high Mr
How does branching of a polymer chain affect its boiling point?
Polymers with more branches cannot pack as closely as those without so the van der Waal’s forces between chains are weaker
How can you turn an alkene into an alkane?
Add H2 in the presence of a nickel catalyst
