Halogenoalkanes

Question 1

Define a nucleophile

Answer 1

A species which donates an electron pair

Question 2

Explain the mechanism for the hydrolysis of halogenoalkanes

Answer 2

Hydrolysis is heterolytic bond breaking by action of water.
OH- nucleophile which attacks the slightly positive carbon.
Substitutes the halogen for an OH and therefore hydrolyses the compound.

Question 3

Explain the threat to the ozone layer for the free radical substitution of CFCs

Answer 3

CFCs are released into the atmosphere from aerosols. They are so unreactive that they don’t break down until they reach high enough in the atmosphere. The UV rays here cause Homolytic fission (free radical substitution) which causes ozone depletion and allows more harmful UV rays to reach the surface:

CF2Cl2 —> CF2Cl• + Cl•
•Cl + O3 —> ClO• +O2
•ClO + O —> Cl• + O2
O + O3 —> 2O2

Question 6

Explain the method one would use for testing the rates of reaction for halogenoalkanes

Answer 6

We can estimate the rates of reaction by reacting the RX with aqueous AgNO3 in ethanol to form a cloudy ppt
The quicker the ppt is formed, the weaker the bond.

Question 8

Explain the intermolecular bonding within halogenoalkanes

Answer 8

They take part in London dispersion and permanent dipole dipole interactions but not hydrogen bonding. Therefore they are immiscible in water due to lack of h bonding and low polarity