Haloalkanes

Question 1

How to do classify a haloalkane?

Answer 1

Primary- 1 R group of the C atom with the halogen
Secondary- 2 R groups
Tertiary- 3 R groups

Question 2

What is the overall reaction equation of hydrolysis of a haloalkane, what type of reaction is it, what is the reagent, what are the conditions and what is formed?

Answer 2

RX+ OH- (aq) -> ROH + X(aq) 
Reagent- dilute NaOH (aq) 
Conditions- heat under reflux
Type- nucleophilic substitution
Alcohol is formed

Question 3

Describe the mechanism for the nucleophilic substitution (hydrolysis) of a haloalkane?

Answer 3

Dipole between C-X (X being partially neg and C being partially pos)
OH with lone pair and neg charge
Curly arrow from lone pair from OH to C partially pos
Curly arrow from C-X bond to X partially neg
Leads to alcohol and X with lone pair and neg charge

Question 4

Why does OH attack the Carbon attached to the X?

Answer 4

OH = nucleophile so attacks the electron deficient C to donate a pair of electrons and forms a covalent bond

Question 5

What is another example of a nucleophile that is used in hydrolysis? Why is it not used as much?

Answer 5

Water- weak necleophile so too slow therefore not efficient way of making an alcohol

Question 6

What is the reaction equation for hydrolysis of a haloalkane using water?

Answer 6

RX+ H2O -> ROH + H+ + X-

Question 7

What can be used to compare the rate of hydrolysis in different haloalkanes? Why?

Answer 7

AgNO3 in ethanol
Ethanol acts as a solvent dissolving the haloalkane and AgNO3
AgNO3 reacts with the X- to form a precipitate AgX (s)

Question 8

What are the potential precipitates that form and which do you predict is the fastest, when a X- reacts with AgNO3?

Answer 8

AgCl -white and slowest
AgBr- cream
AgI- yellow and fastest
AgF is soluble in water so can’t be tested

Question 9

What are the properties of a C-F bond compared to a C-I bond?

Answer 9

C-F= shorter 
Less reactive
Highest bond enthalpy
Strongest bond- due to less shielding, stronger attraction between the nuclei and shared pair of electrons
C-Cl
C-Br 
C-I (opposite)

Question 10

Which haloalkane is the most and least reactive?

Answer 10

Fluoroalkanes- least reactive as C-F bond is strongest due to highest bond enthalpy
Iodoalkanes- most reactive as C-I bond is the weakest due to lowest bond enthalpy

Question 11

What are CFCs and what were they developed for?

Answer 11

ChloroFluoroCarbons

Use as refrigerants aerosols and blowing agents

Question 12

What are the advantages and disadvantages to CFCs?

Answer 12

Pros- low reactivity
-high volatility
Cons- damage to ozone layer

Question 13

How do CFCs damage the ozone layer?

Answer 13

CFCs are stable gases (due to strong C-X bonds) so diffuse through atmosphere until they reach the ozone layer.
UV radiation breaks the C-Cl bond releasing Cl radicals which remove O3 molecules creating a hole in the ozone layer allowing UV radiation through the surface

Question 14

How do the Cl radicals remove O3 molecules?

Answer 14

Initiation( due to UV radiation)
C2F2Cl2-> C2F2Cl. + Cl.
Propagation:
Cl. + O3 -> ClO. + O2 removes ozone
ClO. + O -> Cl. + O2 regenerates Cl.

Overall O3 + O -> 2O2

Question 15

How are nitrogen oxide radicals produced and using equations how do they remove ozone?

Answer 15

Aircraft emissions and lightning
.NO + O3 -> .NO2 + O2
.NO2 + O -> .NO + O2

Overall: O3 + O -> 2O2

Question 16

What molecules are present in the ozone layer and what is its job?

Answer 16

O3, O2 and O

Protect the earth by absorbing UV radiation.

Question 17

How is O3 continually being formed and broken down by UV radiation?

Answer 17

Absorption of UV-C
O2 -> 2O
Which react to form O3
O2 + O -> O3
O3 then absorbs UV-B
O3 -> O2 + O

O2 + O -> O3