Alkenes

What does a double bond consist of?

A sigma bond and a pi bond

What is a sigma bond?

A direct overlap of orbitals between bonding atoms, it consists of a pair of electrons

What is a pi orbital?

The sideways overlap of two adjacent p-orbitals above and below carbon atoms (in the bond)

Which type of bond is weaker?

Pi bond.

What is an unsaturated hydrocarbon?

• At least one C=C bond

• Contains only C and H

Features of alkenes

• Similar chemical properties

• Same general formula (C_nH_2n)

• Same functional group (C=C)

• Sucessive members differ by CH₂

• Graduation in physical properties

Why are alkenes more reactive than alkanes?

• Pi bond is weaker than sigma bond

• C=C is a region of high electron density (attracts elecctrophiles)

What is an addition reaction?

One product formed

What is hydrogenation?

The addition of hydrogen

What are the conditions require for hydrogenation of an alkene?

Ni catalyst at 150*C

What is halogenation?

Addition of a halogen

What are the conditions required for halogenation?

An inert solvent

What is the chemical test to distinguish between an alkane and alkene?

• Add bromine to both samples

• Cover test tubes with foil

• Leave to react

• In alkene bromine will be decolorised

• Alkane = no color change

What is hydration?

Addition of water

What are the conditions needed for hydration of an alkene?

• H₃PO₄ catalyst

• 65 atm

• 300*C

Why are hydration reactions important?

Produce alcohol (industrial production of ethanol)

Conditions needed for the addition of hydrogen halides?

Inert solvent, RTP