Haloalkanes- ORGANIC I P2 Flashcards
The mechanism for the reaction of fluorine with either an alkane or a
fluoroalkane is similar to that for the reaction of chlorine with methane.
Name the type of mechanism for the reaction of chlorine with methane.
(Free-) radical substitution
Write equations for the following steps in the mechanism for the reaction of
fluorine with fluoromethane (CH3F) to form difluoromethane (CH2F2).
Initiation
Propagation
Termination
Initiation
F2 –> 2F*
Penalise absence of dot once only
First propagation
F* + CH3F –> *CH2F + HF
Penalise + or − charges every time
Second propagation
F2 + CH2F –> CH2F2 + F
Accept dot anywhere on CH2F radical
Mark independently
Termination (must make 1,2-difluoroethane)2 *CH2F
CH2FCH2F
Write an overall equation for the reaction of fluorine with ethane to form
pentafluoroethane (CF3CHF2) by this mechanism.
CH3 CH3 + 5F2 –> CF3CHF2 + 5HF
(C2H6)(C2HF5)
Give the IUPAC name for CCl3CF2Cl
1,1,1,2-tetrachloro-2,2-difluoroethane
Accept phonetic spelling eg “fluro, cloro”
Penalise “flouro” and “floro”, since QoL
OR
1,2,2,2-tetrachloro-1,1-difluoroethane
Nitrogen monoxide (NO) catalyses the decomposition of ozone into oxygen.
Write the overall equation for this decomposition.
2O3 —> 3O2
Use the overall equation to deduce Step 3 in the following mechanism that
shows how nitrogen monoxide catalyses this decomposition.
Step 1 O3 –> O + O2
Step 2 NO + O3 –> NO2 + O2
Step 3
Chlorine can be used to make chlorinated alkanes such as dichloromethane.
(a) Write an equation for each of the following steps in the mechanism for the reaction
of chloromethane (CH3Cl) with chlorine to form dichloromethane (CH2Cl2).
Initiation
Propagation
Termination
When chlorinated alkanes enter the upper atmosphere, carbon-chlorine bonds are
broken. This process produces a reactive intermediate that catalyses the
decomposition of ozone. The overall equation for this decomposition is
2O3 –> 3O2
(i) Name the type of reactive intermediate that acts as a catalyst in this reaction.
Write two equations to show how this intermediate is involved as a catalyst in
them decomposition of ozone.
The reaction is a free-radical substitution reaction similar to the reaction of methane
with chlorine.
(i) Write an equation for each of the following steps in the mechanism for the
reaction of CHF3 with Br2
In the upper atmosphere, it is more likely for CBrF3 to produce bromine atoms
than it is for CClF3 to produce chlorine atoms.
Suggest one reason for this.
Bromine atoms have a similar role to chlorine atoms in the decomposition of
ozone.
The overall equation for the decomposition of ozone is
2O3 –> 3O2
Write two equations to show how bromine atoms (Br*) act as a catalyst in the
decomposition of ozone.
Explain how these two decomposition equations show that bromine atoms
behave as a catalyst.
In some refrigeration systems, CHF3 has replaced CClF3 because of concerns about
ozone depletion.
(i) Identify the species formed from CClF3 that is responsible for the catalytic
decomposition of ozone in the upper atmosphere.
Write an overall equation to represent the decomposition of ozone into oxygen.
Define structural isomers
Same molecular formula
Different structural formula
