OCR A Chemistry F324 Rings, Polymers and Analysis Thu 26 Jan 2012

Reply 40

The medjai

Original post by LifeIsGood

I'm stuck on the exam questions, I don't know how to tackle them :frown:

Post the question on here.

Reply 41

LifeIsGood

12

Original post by The medjai

Post the question on here.

January 2011 Paper Q6

Reply 42

The medjai

Original post by LifeIsGood

January 2011 Paper Q6

Ah, this gastly question. To be honest i've no idea how to answer because i've never encountered that type of structure before. You could go straight to the mark scheme but i'd doubt if it would make any sense. Do you mind if I do abit more research and get back to you?

Reply 43

silver0

1

I'm so shocked that so many people on here have finished the syllabus for the January exam.. I have only done the Rings, and Analysis sections.. just finished the NMR, it's so confusing. I feel like my teacher is teaching too slow, we only got like a month but she might still be teaching in January where it should really be used to go through past papers etc..

Reply 44

LifeIsGood

12

Original post by The medjai

Ah, this gastly question. To be honest i've no idea how to answer because i've never encountered that type of structure before. You could go straight to the mark scheme but i'd doubt if it would make any sense. Do you mind if I do abit more research and get back to you?

That'll be very helpful :smile:

Thank you so much

Reply 45

fudgesundae

16

bit early aren't we? I wasn't going to even start thinking about this exam until oxford interviews are out of the way lol.

Reply 46

fudgesundae

16

Original post by silver0

I'm so shocked that so many people on here have finished the syllabus for the January exam.. I have only done the Rings, and Analysis sections.. just finished the NMR, it's so confusing. I feel like my teacher is teaching too slow, we only got like a month but she might still be teaching in January where it should really be used to go through past papers etc..

Really? This is a really short module, we had it finished just before half term.

Reply 47

LifeIsGood

12

Went over a paper and just messed up so many marks, really need to focus and start revising for this exam properly, the main thing I want is to not resit it in summer, I have enough exams :/

Reply 48

arvin_li

SOme people on TSR got full mark on this unit last june !! could you be a legend and explain to us how! just doing textbook and past papers wont do much (only in this unit tho) ..am telling you cuz it didnt work for me ..might work for you
ANyone knows where we can find some decent questions

Reply 49

DoDoBeDo

This is pretty much the only module that's really clicked with me. We did the January 2011 paper in class last week & got 90% (next highest grade in the class was 71% so yeh.)

But maybe it's because I'm the only person in the class who likes NMR...

I'm just really struggling with those 'extra' questions, like when you have to speculate the impurity or what it was reacted with when all you have is words. It just seems a lot of work for 1 mark!

Really want an A on this paper. :biggrin:

Hoping if I carry on like I am I can achieve that.

Reply 50

LifeIsGood

12

Original post by DoDoBeDo

This is pretty much the only module that's really clicked with me. We did the January 2011 paper in class last week & got 90% (next highest grade in the class was 71% so yeh.)

But maybe it's because I'm the only person in the class who likes NMR...

I'm just really struggling with those 'extra' questions, like when you have to speculate the impurity or what it was reacted with when all you have is words. It just seems a lot of work for 1 mark!

Really want an A on this paper. :biggrin:

Hoping if I carry on like I am I can achieve that.

Can you help me please? :frown:

I'm struggling with this paper. How do you tackle any NMR question? They're must be a step to step guide just to analyse it all, the markschemes aren't very helpful

Reply 51

DoDoBeDo

Original post by LifeIsGood

Can you help me please? :frown:

I'm struggling with this paper. How do you tackle any NMR question? They're must be a step to step guide just to analyse it all, the markschemes aren't very helpful

It's really hard to explain. Everyone learns differently. For example last week our teacher gave us a molecule and asked us to draw both the carbon-13 and proton NMR. Working backwards really helped some people. So maybe picking a molecule, drawing what you think would be the NMR and then googling the actual NMR to compare what you got to the actual thing?

But I'm going to give you a run down of how I work. Sorry if this gets very long & I might well confuse you more or say something wrong. (It's my 18th tomorrow. I'm partying with wine and textbooks) :lol:

Carbon 13

•

Peaks correspond to environments. (if there are 4 peaks on a spectrum there are 4 environments in the molecule.)

•

There can be more than 1 peak in the same chemical shift range, it just means it could be the same thing in a different environment (attached to something different. it could be a CH2 attached to a C2H5 rather than a CH3 for example :smile: )

•

The height of peaks corresponds to relative abundance of that particular environment (sometimes there are numbers above the peaks? Basically if it's 1, 1, 1, 2 - the one with 2 in has 2 carbons in the same environment compared to 1 in the other three)

•

Chemical Shift is just what that carbon is attached to.

When given a question. Count the number of environments in each molecule first. (be careful. What you may think are the same are different & vice versa). Then count peaks. That should rule out a fair few - sometimes leaves you with 1, sometimes it leaves you with 2 or 3. That's when you go to size of peaks. Sometimes that can rule 1 out :smile:

(there can be 4 equally sized peaks or 3 smaller & 1 larger. 4 equal means that there are 4 environments with the same amount of carbons in them)

Proton

•

Peaks, again, correspond to different environments

•

Peaks will appear at the chemical shift for the environment they're in

•

But the splitting is due to the n+1 rule. Where N=Number of Hydrogens on Adjacent Carbons. It splits into n+1 peaks :smile:

•

Again, the height/area under the peak is relevant to the number of hydrogens in the same environment. You can be given numbers above peaks or an integration trace which will tell you in which ratio :smile:

•

OH & NH peaks will always be singlets as the H is not attached to a carbon

Label up the spectra! Write how many it's split in to & how many H's must be on adjacent carbons.
Look at where it is. a shift at ~3.8 split into 3, it means that it's HC-Cl (or something) and attached to CH2 :smile:

.

Gonna shut up now because I'm nervous :tongue:

This Website is really good at giving a walk through of NMR. (and all other spectroscopy), it's probably done it far better than I ever could or have or will try to again :tongue:

Also google Spectra School (RSC affiliated thing) it's meant to be really good (I can't access it personally as my Java has ballsed up!)

If you drop me a PM or whatever I'll always try and give a better, more exact, answer to any questions :smile:

(edited 12 years ago)

Reply 52

LifeIsGood

12

Original post by DoDoBeDo

It's really hard to explain. Everyone learns differently. For example last week our teacher gave us a molecule and asked us to draw both the carbon-13 and proton NMR. Working backwards really helped some people. So maybe picking a molecule, drawing what you think would be the NMR and then googling the actual NMR to compare what you got to the actual thing?

But I'm going to give you a run down of how I work. Sorry if this gets very long & I might well confuse you more or say something wrong. (It's my 18th tomorrow. I'm partying with wine and textbooks) :lol:

Carbon 13

•

Peaks correspond to environments. (if there are 4 peaks on a spectrum there are 4 environments in the molecule.)

•

There can be more than 1 peak in the same chemical shift range, it just means it could be the same thing in a different environment (attached to something different. it could be a CH2 attached to a C2H5 rather than a CH3 for example :smile: )

•

The height of peaks corresponds to relative abundance of that particular environment (sometimes there are numbers above the peaks? Basically if it's 1, 1, 1, 2 - the one with 2 in has 2 carbons in the same environment compared to 1 in the other three)

•

Chemical Shift is just what that carbon is attached to.

When given a question. Count the number of environments in each molecule first. (be careful. What you may think are the same are different & vice versa). Then count peaks. That should rule out a fair few - sometimes leaves you with 1, sometimes it leaves you with 2 or 3. That's when you go to size of peaks. Sometimes that can rule 1 out :smile:

(there can be 4 equally sized peaks or 3 smaller & 1 larger. 4 equal means that there are 4 environments with the same amount of carbons in them)

Proton

•

Peaks, again, correspond to different environments

•

Peaks will appear at the chemical shift for the environment they're in

•

But the splitting is due to the n+1 rule. Where N=Number of Hydrogens on Adjacent Carbons. It splits into n+1 peaks :smile:

•

Again, the height/area under the peak is relevant to the number of hydrogens in the same environment. You can be given numbers above peaks or an integration trace which will tell you in which ratio :smile:

•

OH & NH peaks will always be singlets as the H is not attached to a carbon

Label up the spectra! Write how many it's split in to & how many H's must be on adjacent carbons.
Look at where it is. a shift at ~3.8 split into 3, it means that it's HC-Cl (or something) and attached to CH2 :smile:

.

Gonna shut up now because I'm nervous :tongue:

This Website is really good at giving a walk through of NMR. (and all other spectroscopy), it's probably done it far better than I ever could or have or will try to again :tongue:

Also google Spectra School (RSC affiliated thing) it's meant to be really good (I can't access it personally as my Java has ballsed up!)

If you drop me a PM or whatever I'll always try and give a better, more exact, answer to any questions :smile: