The Student Room Group

Chem help

Draw mechanism for reaction of 1,1 - dichloroethane with chlorine to form 1,1,2,2 -tetrachloroethane ( using uv light ).

Scroll to see replies

what have you got so far?
And what does this mean For every H atom replaced by F / Cl/ Br / I, one molecule of F2 / Cl2 / Br2 / I2is used and one molecule of HF / HCl/ HBr / HI is released.
So I've done cl2-> 2cl.
Ch3ch3 + cl. -> hcl + ch3ch2.
ch3ch2. + cl2 -> ch3ch2cl + cl.
Ch3ch2cl. + cl. -> ch3ch2cl
Ch3ch2. + ch3ch2. -> ch3ch2ch2ch3
Free rad sub

I don't get the diff between balanced equations and the mechanism itself
for the mechanism, you're going to have 3 key steps: initiation, propagation, and termination

https://www.chemguide.co.uk/mechanisms/frmenu.html
chemguide has some decent explanations on the topic and if you scroll to the bottom of each page there are some links to more explanations and examples
Yh but what's the balanced eq thing asking for
Original post by Roxibox123
So I've done cl2-> 2cl.
Ch3ch3 + cl. -> hcl + ch3ch2.
ch3ch2. + cl2 -> ch3ch2cl + cl.
Ch3ch2cl. + cl. -> ch3ch2cl
Ch3ch2. + ch3ch2. -> ch3ch2ch2ch3


the question is asking for the reaction mechanism of 1,1-dichloroethane with chlorine to form 1,1,2,2-tetrachloroethane, using uv light

so a few things:
it might make it clearer to separate the different stages of the mechanism: initiation, propagation, termination
the question refers to UV, so make it clear in your answer where UV is involved
look at the product the question is asking for. yes, other products will form as well, but in your answer you just want to show the formation of 1,1,2,2-tetrachloroethane. I find it helps to draw out the structural formula of the reactant (1,1-dichloroethane) and the product (1,1,2,2-tetrachloroethane) to help identify where the changes occur.

have a look at the page for multiple substitutions in the methane/chlorine reaction
https://www.chemguide.co.uk/mechanisms/freerad/multisubcl.html
Original post by Roxibox123
Free rad sub

I don't get the diff between balanced equations and the mechanism itself


usually, for organic reaction mechanisms (such as a nucleophilic substitution reaction (see https://www.chemguide.co.uk/mechanisms/nucsub/hydroxide.html for examples, equations and mechanisms) bit of a random example) you would have

the balanced equation
e.g. CH3CH2CH2CH2Br + OH- ––> CH3CH2CH2CH2OH + Br-
(or CH3CH2CH2CH2Br + NaOH ––> CH3CH2CH2CH2OH + NaBr)
you're showing the overall results of the reaction it tends to show only reactants ––> products, no curly arrows or whatever

and the mechanism
which involves curly arrows etc. you're showing what happens during the reaction, where species attack and so on
it may have multiple steps (i.e. reactants ––> intermediates ––> products)


apologies for linking chemguide so much! I find that it has a bunch of good explanations and examples so it tends to be my go-to for looking up chemistry-related things
(edited 1 year ago)
the mechanism is the initiation, propagation and termination steps.

dichloroethane + chlorine ------- trichloromethane so you will have to go through this process twice. Then

trichloroethane + chlorine ------- tetrachloromethane to get the final product I think!

You will have to assume that the addition of chlorine is on separate carbon atoms in the chlorinated ethane molecule. Not sure if it gives more than chemguide but try:

https://chemrevise.org/revision-guides/

https://science-revision.co.uk/A-level_organic_free_radical_substitution.html
U know if I was doing electorfphilic addition propene with hbr then does it matter whether I put the Br at the end or do I have to put it in the middle. How do u know where ur supposed to put it 20E71612-4637-4C92-950D-B34C739BE268.jpg.jpeg
Where do u put the Br in electoephilic addition after the foundling bond breaks.
^ double. Like am I supposed to put it at the end or the middle or somewhere else A905BDE7-D235-46BA-B688-4EF9391A83A5.jpg.jpeg
How do u do butan2ol with Sulfuric acid and potsssium dichromate under reflux

Do u do the sulfuric part first and then alcohol or alcohol - lakebed and the sumfuric acid
Original post by Roxibox123
Where do u put the Br in electoephilic addition after the foundling bond breaks.


Original post by Roxibox123
^ double. Like am I supposed to put it at the end or the middle or somewhere else A905BDE7-D235-46BA-B688-4EF9391A83A5.jpg.jpeg


the major product forms via the more stable carbocation
which means that (for the major product) the bromine will attach to the carbon (from the double bond) that is attached to more carbons
so for CH2=CH–CH3 + H–Br
the major product would be CH3–CHBr–CH3, and the minor product would be CH2Br–CH2–CH3


again, see chemguide for some better explanations than I could give:
https://www.chemguide.co.uk/mechanisms/eladdmenu.html
which has a link to https://www.chemguide.co.uk/mechanisms/eladd/unsymhbr.html
which has a link to https://www.chemguide.co.uk/mechanisms/eladd/unsymhbrtt.html
Original post by Roxibox123
How do u do butan2ol with Sulfuric acid and potsssium dichromate under reflux

Do u do the sulfuric part first and then alcohol or alcohol - lakebed and the sumfuric acid


can you identify what type of alcohol butan-2-ol is? (primary, secondary or tertiary?)

what do you know about the oxidation of alcohols?
handy little link (chemguide again) https://www.chemguide.co.uk/organicprops/alcohols/oxidation.html

see where you can get to from here
What's the ph of 10gdm-3 hcl
Like how do u work it out
Do u just work out the mr
Then do moles is mass over mr
But where's the mass
Original post by Roxibox123
What's the ph of 10gdm-3 hcl


remember that pH = -log[H+]

HCl is a strong acid, meaning that it will fully dissociate (into H+ and Cl-) in water

so can you work out the pH?

Quick Reply

Latest