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AQA CHEM4 and CHEM5 revision thread 2016

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Original post by haj101
To be safe, yes they can be sneaky...


(i) Outline a mechanism for the dehydration of butan-2-ol into but-l-ene.
this for example^. its not in the book is it?
Original post by twallien
Yeah, you need a polar solvent in order to dissolve the sample. If you imagine trying to put oil (long chain hydrocarbons) in water, it wont mix. D2O is basically water (Deuterium being an isotope of Hydrogen).


Hi just a question, when do you no when to use ccl4 as a reagent in nmr stuff and when do you say sic4h12 ? Thanks :smile:


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I've noticed there are a lot of reactions in Organic Synthesis topic that include reflux. Does anyone know which ones do? Every textbook says a different thing???
Original post by Lilly1234567890
(i) Outline a mechanism for the dehydration of butan-2-ol into but-l-ene.
this for example^. its not in the book is it?


Chances are very low tbh but we can trust AQA to sneak in anything tbh...
There's not been any papers- to my knowledge which actually asked to draw out the mechanism however they have asked for the name a number of times.
They may/may not ask us it best to go over it again
It's not in revision guides no but go over it just in case! :smile:
Original post by Sexybadman
Hi just a question, when do you no when to use ccl4 as a reagent in nmr stuff and when do you say sic4h12 ? Thanks :smile:


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Si(CH3)4 is the compound used as the standard for which we can compare the peak the the other ones

CDCL3 is a solvent used to allow the other compounds to dissolve in it.
(In the exam they'll either say/ compound/solvent/standard so be careful!)
Original post by haj101
Si(CH3)4 is the compound used as the standard for which we can compare the peak the the other ones

CDCL3 is a solvent used to allow the other compounds to dissolve in it.
(In the exam they'll either say/ compound/solvent/standard so be careful!)


Awesome cheers for that :smile:


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Original post by Lilly1234567890
(i) Outline a mechanism for the dehydration of butan-2-ol into but-l-ene.
this for example^. its not in the book is it?


I'm pretty sure you don't need to know it. Although search dehydration of ethanol and there's a mechanism on chemguide. We don't need to know the mechanism, just the reaction and the products + conditions.
Original post by _bob_
Could anyone explain this buffer question?


With basic buffers, you need something that dissociates to the thing your weak base becomes when it is protonated/when it deprotonates water (similar to with acidic buffers if you have HA->H+A-, you need something that gives lots of A-, e.g. NaA). Therefore, in this question, where CH3CH2NH2 + H2O <=> CH3CH2NH3+ + OH-, you need a salt that gives CH3CH2NH3+, therefore you need CH3CH2NH3Cl. The CH3CH2NH3Cl will produce lots of CH3CH2NH3+ in solution that can resist changes in pH. Lol I hope that made sense, if not, sorry haha.. hopefully you've found out why the answer is this by now. :tongue:
How do you name this please?

ImageUploadedByStudent Room1465817589.215129.jpg


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Methylethyl 3-methylbutanoate
(edited 7 years ago)
Original post by NobodyCares
Methylethyl 3-methylbutanoate


Thanks, so you don't group the two methyl groups with the prefix dimethyl?


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AHHHHH Help. I cant memorise A2 mechanims :frown:
Hi guys
I need help with part c
I don't understand how you get the orders

Thank you

ImageUploadedByStudent Room1465821261.739736.jpg


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Original post by Glavien
Thanks, so you don't group the two methyl groups with the prefix dimethyl?


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wait, can it also be 3-methylbutanoate propan-2yl. ? what is the correct answer?
Original post by Bloom77
Hi guys
I need help with part c
I don't understand how you get the orders

Thank you

ImageUploadedByStudent Room1465821261.739736.jpg


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If the overall order is 2, then you know the only options you have are:
- 1st order for A and 1st order for B,
- 2nd order for A/B and 0 order for the other.
If the conc. of A triples and the rate increases ninefold, you know A must be 2nd order (i.e. 3^2). This means B HAS to be 0 order, or else you'd have an overall order of 3 for the reaction.
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mbh16
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Original post by Sexybadman
Hi just a question, when do you no when to use ccl4 as a reagent in nmr stuff and when do you say sic4h12 ? Thanks :smile:


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The CCl4 is a solvent and the TMS is used as a standard. When the question asks for a standard say the TMS and if they ask for a solvent then say CCl4 or CDCl3
Can anyone please help with this question ??
Question 1e on June 10, I havent a clue what a trimer is or how to draw one :smile: Thank you !

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-QP-JUN10.PDF
Reply 137
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mbh16
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Screen Shot 2016-06-13 at 15.08.17.png Can someone explain this for me?, i have never seen a question like this before.
Original post by mbh16
Screen Shot 2016-06-13 at 15.08.17.png Can someone explain this for me?, i have never seen a question like this before.


Reducing agent H2/Ni- to protonate the inner ring

CH2

goes from 120 to 109.5
Reply 139
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mbh16
2
Original post by alevelup
Can anyone please help with this question ??
Question 1e on June 10, I havent a clue what a trimer is or how to draw one :smile: Thank you !

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-QP-JUN10.PDF


A trimer is a polymer with only 3 monomers in it, the answer to this question is basically the product formed in step 3 but with an extra monomer of ethanal added.
so it should look like this i think: Screen Shot 2016-06-13 at 15.26.50.png

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