Alkenes 4.1.3 Flashcards
(36 cards)
What is the general formula for alleges?
CnH2n
How does the double bond affect alleges reactivity, why?
It makes them more reactive, the carbon carbon double bond is a region of high electron density
What two distinct bonds make up the double bond in alkenes? Define each bond.
Sigma bond - overlap of orbitals between C atoms
Pie bond - sideways overlap of p-orbitals, adjacent p-orbitals above and below bonding (4 atoms)
What bond angle is present around carbon carbon double bonds?
120• , only 3 bonding regions.
Define a structural isomer.
The same molecular formula but a different structural formula.
Define a stereoisomer
Molecules with the same structural formula but a different arrangement in space.
What are the two thins that are needed for a stereoisomer to form? What are the two types of stereoisomers and how do they differ?
- Carbon carbon double bond
- Different groups attached to each carbon in the double bond
E - even, the heaviest groups are on opposite sides
Z - same, the heaviest groups are on the same side
How do we name alkenes and when must numbering be introduced?
___ene
Once you get to but. Eg but-2-ene
Why are alkenes more reactive than alkenes?
Because of the relatively low bond Enthalpy of the pie bond.
Write a word equation for the hydrogenation reaction. What are the necessary reagents and conditions for this reaction?
Alkene + H2 ➡️ Alkane
•Hydrogen
•Nickel Catalyst (finely divided)
•High Temp.
When is hydrogenation used in the industry?
Manufacturing of margarine.
Write an equation for halogenation. What are the necessary reagents and conditions for this reaction?
Alkene + X2 ➡️ Haloalkane
•Cl2, Br2, I2
•Room temp
•Non-polar solvent, eg. CCl4
If you added bromine water to a halogenation reaction what colour change would be seen?
Orange/brown to colourless. As the alkene turns to a haloalkane.
During halogenation reactions where do the halogens go in the alkene?
On either side of the double bond.
Write an equation for the addition of hydrogen halides. What are the reagents and the conditions for this reaction?
Alkene + HX ➡️ Haloalkane (mono)
- HCl or HBr or HI
- Room Temperature
- Non-polar solvent e.g CCl4
How does reactivity of the hydrogen halides change from HF to HI? Why?
It increases. Bond strength decreases as they are easier to break therefore they are more reactive.
How are minor and major products formed?
When unsymmetrical alkenes react with hydrogen halides or other non symmetrical molecules.
Write a general word equation for hydration. What are the conditions and the reagents?
Alkene + water ➡️ Alcohol
•Steam (H2O)
600K (Temp>100•)
•60 atm
Phosphoric acid catalyst (H3PO4)
(2 products if an unsymmetrical alkene.
What is the main mechanism that we study for alkenes called?
Electrophilic addition
Define an electrophile
An electron pair acceptor.
What is a carbocation?
A positively charged ion formed during electrophilic addition it is an intermediate molecule.
What is Markovinikovs rule?
When a compound HX is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon with the most hydrogen a attached to it already.
How do you decide where to add the H when you react the alkene with compound HX?
Add it to the carbon which has the most H atoms directly attached to it.
Define a polymer
Polymers are long chained molecules made by the joining of many small chained molecules called monomers.
