4.2.2 Haloalkanes: Module 4: Core Organic Chemistry: Chemistry OCR A A Level

What are haloalkanes?

Saturated organic compounds that contain carbon atoms and at least one halogen atoms.

Are halogenoalkanes soluble in water?

Insoluble as C-H bonds are non-polar, not compensated for enough by C-X bond polarity.

Do halogenoalkanes have a polar bond? Why?

Yes polar, as halogen has a higher electronegativity than C (halogen is δ-, carbon is δ+).

What type of intermolecular forces do they have? Why?

Permanent dipole-dipole and London forces of attraction C-X bond polarity creates permanent dipoles.

When would they have higher boiling points?

Increase Carbon chain length. Halogen further down group 7.

How would the mass of a haloalkane compare with the mass of an alkane of the same chain length?

Greater as mass of halogen > mass of H

What is the most important factor in determining halogen reactivity?

The strength of carbon halogen bond.

What would bond polarity suggest the order of reactivity would be?

C-F would be most reactive as most polar bond.

What would bond enthalpies suggest the order of reactivity would be?

C-I would be most reactive as lowest bond enthalpy.

What is a primary halogen?

The halogen atom is present at the end of the chain.

Define nucleophile.

Electron pair donor.

Give 3 examples of nucleophiles.

:OH-

:CN-

:NH3

What is nucleophilic substitution?

A reaction where a nucleophile donates a lone pair of electrons to δ+ C atom, δ− atom leaves molecule (replaced by nucleophiles).

What is hydrolysis?

A reaction where water is a reactant.

What reactant often produces hydroxide ions for hydrolysis?

Water

What fission does water undergo to produce OH-?

Heterolytic fission.

What are CFCs?

Chlorine-fluoro-carbons - haloalkanes containing C, F and Cl only (no H).

What is the problem with CFCs?

Although unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution.

What is the main function of ozone layer?

Provides protection from harmful UV radiation.

Does ozone play a protection role in all layers of the atmosphere?

No, in the troposphere it contributes towards photochemical smog.

How do CFCs break the ozone layer down?

Free radical substitution.

Write an equation for the overall decomposition of ozone into oxygen (O2).

2O3 → 3O2