Alkenes

What are unsaturated hydrocarbons?

Hydrocarbons with a C=C bond

Why are alkanes vulnerable to attack by electrophiles?

The C=C bond consists of one pi bond and one sigma bond

• Pi bonds are exposed and have high electron density

• They attract electrophiles, which are electron deficient

What are electrophiles?

An electron pair acceptor

Outline the electrophilic addition reaction of bromine and alkenes

Outline the electrophilic addition reaction between HBr and alkenes

Which atom from the electrophile goes to the C⁺ ?

The atom with the negative partial charge

• i.e. the more electronegative atom

When can 2 products from electrophilic addition form?

When the alkene is unstable

How do you know which product is major and minor?

The major product is formed via the more stable carbocation

How do you know if a carbocation is more stable or less stable?

Tertiary carbocations are most stable

Primary carbocations are least stable

Why are tertiary carbocations most stable?

They have the most amount of methyl groups that release electrons, reducing the charge on the carbocation, which stabilises it.

Outline the mechanism for the electrophilic addition reaction between H₂SO₄ and Alkenes

How can you test to see if an alkene was produced?

Add bromine water

• Alkenes decolourise bromine water from orange to colourless

Outline how to draw the addition polymer from an alkene monomer

When do you add ‘n’ to the brackets?

If the question asks to draw ‘repeating units’

DON’T ADD ‘n’ if the question asks to draw one repeating unit

What are the uses of PVC?

Window frames coverings and gutterings

Why is PVC rigid in its pure form?

It has strong dipole-dipole forces between polymer chains from the C-Cl polar bond

Why is plasticiser added to PVC?

To weaken the dipole-dipole forces, so the chains can move more easily

• Makes the polymer more flexible

What is a use of plasticised PVC?

Insulation for wiring