Haloalkanes.

Question 1

Explanation of polarity of the Carbon-halogen bond.

Answer 1

Halogen atoms are more electronegative than carbon atoms.
Electron pair in C-Halogen bonds is closer to halogen atom than carbon atom.

Question 2

Nucleophile definition and relevance to haloalkanes.

Answer 2

Species that donate a lone pair of electrons.
Carbon atom has slightly positive charge
Attracts nucleophiles
Donates pair of electrons to form new covalent bond to the electron deficient carbon atom.

Question 3

Nucleophilic substitution.

Answer 3

Haloalkane+nucleophile:
nucleophile replaces halogen
New compound made w/ diff functional group

Question 4

Hydrolysis of haloalkanes.

Answer 4

Water/aqueous solution causes bond breaking in a molecule.
Halogen atom replaced by -OH group.
-Nucleophile approaches c atom attached to halogen on opposite side of molecule from halogen atom.
-Direction of attack minimises repulsion between nucleophile and delta minus halogen atom.
-Lone pair of electrons on hydroxide ion is attracted and donated to delta + carbon atom.
-New bond formed between O of hydroxide ion and c atom.
-Carbon-halogen bond breaks by heterolytic fission.
-New product=alcohol+halide ion.
PRACTICE DRAWING MECHANISM.

Question 5

Conditions for hydrolysis of haloalkanes.

Answer 5

Aqueous sodium hydroxide
Heated under reflux to increase speed of reaction.

Question 6

Rate of hydrolysis and carbon-halogen bond strength.

Answer 6

C-F is strongest(highest bond enthalpy)
C-I is weakest
Weaker bonds react faster than stronger bonds
Less energy required to break the C-I bond
Fluoralkanes are largely unreactive-too much energy required to break bonds.
Slowest rate=strongest C-halogen bond.

Question 7

Measuring rate of hydrolysis.

Answer 7

Carry out reaction in presence of silver nitrate.
As reaction takes place, halide ions are produced
React w/ Ag+ ions—>precipitate silver halide
Nucleophile is water, in aqueous silver nitrate
Haloalkanes insoluble in water, presence of ethanol solvent=water and haloalkane can mix to form single solution, not 2 layers.

Question 8

Organohalogen compounds and uses.

Answer 8

Molecules that have at least one halogen atom joined to a carbon chain.
Pesticides, solvents, making polymers, flame retardants, refrigerants.
Not broken down naturally in nature.

Question 9

How do CFCs deplete the ozone layer?

Answer 9

When reach stratosphere, UV gives energy to break bonds by homolytic fission—>radicals
C-Cl bond breaks as lowest enthalpy.

Question 10

Stages of breakdown of CFCs.

Answer 10

CF2CL2–>CF2CL. +Cl.(initiated by UV)
CL.+O3–>ClO.+O2
ClO.+O–>Cl.+O2.

Question 11

Stages of nitrogen oxide radicals ozone breakdown.

Answer 11

NO.+O3–>NO2.+O2
NO2.+O–>NO.+O2
Overall equation for Cl and NO:
O3+O–>2O2.
Nitrigen oxide radicals formed during lightning strikes and aircraft travel.