Topic 3.3 - Haloalkanes

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+)

Which intermolecular forces

do they have? why?

Permanent dipole-dipole and van der Waals

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 their

reactivity?

Carbon-halogen bond enthalpy

What is the order of

reactivity of

halogenoalkanes?

Although C-F is the most polar bond, the bond

enthalpy of C-X decreases down the group, so

reactivity increases down the group

What is a nucleophile?

A negatively charged ion/δ− atom with a lone pair

of electrons which can be donated to an electron

deficient atom

Give 3 examples of

nucleophiles

:OH -

:CN -

:NH 3

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)

Draw the mechanism for the

reaction of bromoethane

with NaOH (aq).

Draw the mechanism for the

reaction of bromoethane

with KCN

Draw the mechanism for the

reaction of bromoethane

with NH

Draw a mechanism for the

reaction of bromoethane

with NaOH in ethanol

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 are CFCs being

replaced with?

HCFCs (hydrogen, chlorine, fluorine, carbon)

HFCs (hydrogen, fluorine, carbon)

What are the conditions/

reactants needed for the

elimination reaction of

haloalkanes?

NaOH or KOH dissolved in ethanol (no water

present)

Heated

What is formed in the

elimination reaction of

haloalkanes?

An alkene, water and halogen ion