Free radical substitution help please!
I need to write the FRS of methane and chlorine to get 1,2,2Tricholorethane. I know how to do the FRS of methane and chlorine to get chloromethane but have no clue how I am meant to get trichloroethane?
Can somebody explain how to do this?
Edited to make more clear
Can somebody explain how to do this?
Edited to make more clear
(edited 5 years ago)
Original post by Leme
I need to write the FRS of methane and chlorine to get Tricholorethane. I know how to do the FRS of methane and chlorine to get chloromethane but have no clue how I am meant to get trichloroethane?
Can somebody explain how to do this?
Can somebody explain how to do this?
The issue with free radicals is that they are sluts, they'll go with anything.
Two methyl free radicals combine to make an ethane molecule (and so on), or a methyl free radical combines with a trichloromethane molecule in a propagation step to make trichloroethane ...
... there are loads of possibilities.
Original post by Samhunt6
If we keep substituting chlorine into methane using the propagation steps, eventually we end up with •CCl3 and if we react this with a •CH3 in the termination step we shall end up with trichloroethane
I should have been more clear with this, my bad. I need to make 1,2,2 trichloroethane so would I not need to react a chloromethane with a dichloromethane?
Original post by Leme
So since its 1,2,2 tricholorethane, i would need to make a 1chloromethane free radical and a dichloromethane free radical and combine them to terminate the reaction.
Would this not take loads of propagation stages?
Would this not take loads of propagation stages?
Yes. Well not lots, but more than one.
Original post by Leme
So since its 1,2,2 tricholorethane, i would need to make a 1chloromethane free radical and a dichloromethane free radical and combine them to terminate the reaction.
Would this not take loads of propagation stages?
Would this not take loads of propagation stages?
not so many...
there are about 100 propagations per termination, so the number is not an issue.
Original post by TutorsChemistry
Yes. Well not lots, but more than one.
I'm really not very good at FRS since i've only done it for one lesson. I've done the FRS to form chloromethane, what do I do after this point? If I terminate the process then I can't get any dichloromethane, but if I carry on with the propagations won't it just change the chloromethane into a dichloromethane even though I need both.
Sorry if i'm talking rubbish, I'm pretty puzzled.
Original post by charco
The issue with free radicals is that they are sluts, they'll go with anything.
Two methyl free radicals combine to make an ethane molecule (and so on), or a methyl free radical combines with a trichloromethane molecule in a propagation step to make trichloroethane ...
... there are loads of possibilities.
Two methyl free radicals combine to make an ethane molecule (and so on), or a methyl free radical combines with a trichloromethane molecule in a propagation step to make trichloroethane ...
... there are loads of possibilities.
The TSR Jessica of organic chemistry.
Termination is uncontrollable, i.e. you can end up with a range of different products. Plus, the mono-substituted product can become a poly-substituted product. I.E. repeated free radical substitution.
The steps are on the pic but I am not sure you can 'choose' which free radicals you want to react together
Original post by Leme
I'm really not very good at FRS since i've only done it for one lesson. I've done the FRS to form chloromethane, what do I do after this point? If I terminate the process then I can't get any dichloromethane, but if I carry on with the propagations won't it just change the chloromethane into a dichloromethane even though I need both.
Sorry if i'm talking rubbish, I'm pretty puzzled.
Sorry if i'm talking rubbish, I'm pretty puzzled.
After the first propogation step 2 things can happen:
A termination step. Not very likely as the concentration of free radicals within the mixture is very very small. (only a tiny proportion of the Cl2 molecules actually cleave to become chlorine free radicals).
or another propogation step. Quite likely as the chlorine free radical is far more likely to collide with another alkane molecule or a chloroalkane molecule than it is to collide with another free radical.
As you can imagine the propogation can theoretically continue until every hydrogen atom on the alkanes has been substituted by chlorine. This is why there are a huge range of possible products.
Original post by charco
The issue with free radicals is that they are sluts, they'll go with anything.
Genius analogy.
Original post by TutorsChemistry
After the first propogation step 2 things can happen:
A termination step. Not very likely as the concentration of free radicals within the mixture is very very small. (only a tiny proportion of the Cl2 molecules actually cleave to become chlorine free radicals).
or another propogation step. Quite likely as the chlorine free radical is far more likely to collide with another alkane molecule or a chloroalkane molecule than it is to collide with another free radical.
As you can imagine the propogation can theoretically continue until every hydrogen atom on the alkanes has been substituted by chlorine. This is why there are a huge range of possible products.
A termination step. Not very likely as the concentration of free radicals within the mixture is very very small. (only a tiny proportion of the Cl2 molecules actually cleave to become chlorine free radicals).
or another propogation step. Quite likely as the chlorine free radical is far more likely to collide with another alkane molecule or a chloroalkane molecule than it is to collide with another free radical.
As you can imagine the propogation can theoretically continue until every hydrogen atom on the alkanes has been substituted by chlorine. This is why there are a huge range of possible products.
So once I've made the chloromethane free radical, what do I do next in order to get the dichloromethane free radical? What do I write on the next propagation, i'm really confused/
Original post by Leme
So once I've made the chloromethane free radical, what do I do next in order to get the dichloromethane free radical? What do I write on the next propagation, i'm really confused/
In the first equation of your next propogation the chloromethane you already made reacts with a chlorine free radical. Try writing the equation for that and then see if you can use FRS logic to work out the second equation.
(The second equation will be where the dichloromethane will be formed)
Original post by Pigster
But, why has no one pointed out that there is no such chemical as "1,2,2Tricholorethane"?
BOOM.
*hangs head in shame*
Edit:
We all missed the naming convention error (which is important).
The chemistry discussed is correct though.
(edited 5 years ago)
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