Haloalkanes

Do haloalkanes have a polar bond?

Yes, all C-X bonds are polar as halogens have a higher electronegativity than carbon

What is the order of polarity of C-X bonds and what determines this?

C-F most polar

C-Cl

C-Br

C-I least polar

F has the highest electronegativity difference to C, which means the C-X has stronger partial charges and the biggest dipole. This decreases down the group.

Are haloalkanes soluble in water? Why?

No, they are insoluble in water as the R group is non-polar

What intermolecular forces do haloalkanes have?

Van der waals forces and permanent dipole-dipole

What can haloalkanes be dissolved in?

Hydrocarbons - as these are non polar

How does chain length affect boiling point of haloalkanes?

Longer chain = higher boiling point

This is because VdW forces and no. of electrons increase with chain length

How does branching affect boiling point in haloalkanes?

Branching reduces boiling point

This is because it decreases the surface area - so VdW forces are weaker

How does boiling point change down the group?

It increases down the group as the halogen is larger so has more electrons and stronger VdW forces

What is the most important factor in determining their reactivity?

C-X bond enthalpy

What's the order of reactivity of haloalkanes?

Reactivity increases down the group

What happens when haloalkanes react with acidified AgNO3?

• Hydrolysis reaction

• C-X bond breaks

• X- ion released into solution

• AgX(s) precipitate formed

What colour precipitates would chlorobutane, bromobutane and iodobutane form when reacted with acidified AgNO3?

• Chlorobutane: white ppt

• Bromobutane: cream ppt

• Iodobutane: yellow ppt

What is a nucleophile?

An electron-rich species with a lone pair of electrons on an electronegative atom which can be donated to form a new covalent bond with an electron-deficient species

Give 3 examples of nucleophiles

:OH-

:CN-

:NH3

What is nucleophilic substitution?

A reaction where a nucleophile donates a lone pair of electrons to an electron-deficient carbon atom and an electron-rich atom leaves the molecule as it is replaced by a nucleophile

What are the reagents and conditions needed for the nucleophilic substitution with :OH-?

Reagent: NaOH/KOH

Conditions: aqueous and ethanol, warm

What are the reagents and conditions needed for the nucleophilic substitution with :CN-?

Reagent: aqueous ethanolic KCN

Conditions: aqueous and ethanol, warm

What are the reagents and conditions needed for the nucleophilic substitution with :NH3?

Reagent: excess conc NH3 solution

Conditions: ethanol and high pressure, excess sol

What is elimination?

A reaction where a large molecule loses atoms or groups of atoms

What nucleophile is used in elimination?

:OH- which acts as a base

What are the reagents and conditions needed for the elimination reaction of haloalkanes?

Reagent: KOH (ethanol)

Condition: heated

What is formed in the elimination reaction of haloalkanes?

An alkene, water and a halogen ion

What's the mechanism for elimination reaction of haloalkanes?

How do you decide whether a haloalkane undergoes nucleophilic substitution or elimination?

It depends on the reaction conditions:

Aqueous NaOH/KOH, warm → nucleophilic substitution

Ethanolic NaOH/KOH, hot → elimination

What are CFCs?

Haloalkanes containing C, F and Cl only (no H)

What is the problem with CFCs?

They catalyse the breakdown of ozone in the atmosphere via free radial substitution

What are CFCs being replaced with?

HCFCs and HFCs