C15 - haloalkanes

Question 1

haloalkane —> alkene + H2O + HX

Answer 1

KOH & ethanol solvent

Question 2

What is a nucleophile?

Answer 2

A species that donates a lone pair of electrons

Question 3

Describe the steps of nucleophilic substitution

Answer 3

1) Nu- attacks & donates an electron lone pair to a +C atom
(travels opposite side to the halogen to avoid repulsion)
2) C-X breaks heterolytically due to new Nu-C bond formatiom
3) New product & halide ion produced

Question 4

Haloalkane –> alcohol + NaX

Answer 4

Hydrolysis
nucleophilic substitution
NaOH & reflux

Question 5

Bond strength

Answer 5

C-F = most polar
strongest
highest bond enthalpy

C-I = least polar
weakest bond enthalpy
most reactive

Question 6

Measuring hydrolysis rate in primary haloalkanes

Answer 6

• AgNO3(aq)
  Ag+ + X- –> AgX(s) precipitate
• nucleophile = water in the AgNO3
• Haloalkanes are insoluble in water, so use ethanol solvent, which allows the water and haloalkane to mix in a single layer
  method:
• 3 test tubes with each haloalkane Cl to I
• mix with AgNO3 & ethanol
• place in water bath 60 degrees along with a test tube containing AgNO3
• allow to reach constant temp
• quickly add 1cm3 AgNO3 to each test tube
• Immediately start timer & record how long it takes for precipitate to form

Question 7

ozone layer equilibrium

Answer 7

O2 + O –> O3

Question 8

what is the ozone layer?

Answer 8

10-40km above earth’s surface
- absorbs UV-B (damaging UV radiation) from the sun
- Depletion of O3 layer causes UV-B to reach earth’s surface
- damaging & can cause skin cancer

Question 9

what are CFCs?

Answer 9

chlorofluorocarbons
- very stable due to strong C-Cl & C-F, but become unstable when reach stratosphere & form free radicals
- upset equilibrium and therefore the rate at which O3 is broken & formed aren’t stable

Question 10

how does NO deplete the ozone layer?

Answer 10

• NO from lightening
  NO. + O3 –> NO2. + O2
  NO2. + O –> NO. + O2

Question 11

How do CFCs deplete the ozone layer?

Answer 11

• C-Cl = lowest bond enthalpy
  Initiation:
  CF2Cl2 –> CF2Cl. +Cl.
  propagation:
  Cl. + O3 —> ClO. + O2
  ClO + O —> Cl. + O2

overall:
O3 + O —> 2O2

Question 12

What are organic halogen compounds used for?

Answer 12

• dry cleaning solvents
• pesticides etc.
• making polymers
• refrigerants