Topic 7:Alkenes Flashcards
Structure of alkenes
Planar
All bonding pairs on carbon have 120 degree angles
Geometrical isomers
Occurs around C–C bonds
Due to the fact that the species around the carbon can’t move
Stereoisomers
Compounds with the same structural formula but different arrangements of bonds in 3D space
Physical properties of Alkenes
- Van der waals are the only intermolecular forces
- Similar properties to those of alkanes
- Melting and boiling point increases with number of C atoms present
Positive inductive effect
The more alkyl groups attached the more stable the molecule is
Explanation of halogens reacting with alkenes (electrophilic) addition
- At any one time a diatomic halogen could form a temporary dipole
This positive charge is attracted to the electron dense double bond in the alkene - This negativity also repels the electrons in the Br2, causing it to become more electronegative
- Same process of nucleophilic addition occurs
Test for alkenes
Add a few drops of bromine water
Will turn orange to clear colourless
Alkene (steam conditions) to alcohol
300 degrees
Phosphoric acid catalyst
60-70 ATM pressure
Why are addition polymers unreactive?
- They are large saturated alkanes
- They have strong covalent bonds
- They are non- polar
Why do polymers have a low boiling/ melting point
They only contain Van der Waals
They can sometimes have side chains
PVC (normal) uses
Plastic bags
Sheeting
Insulation of electrical cables
Hardened PVC uses
- Milk crates
- Buckets
- Bottles
Plasticised PVC
- Push molecules apart
- Intermolecular forces are weaker
- Layers can slide over each other more easily
Hardened PVC
- Pulls the molecules closer together
- Stronger intermolecular forces
- Molecules can’t slide over each other
Which type of E/Z isomerism is more stable
E isomerism
