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OCR F324-June 2013 Chemistry

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Original post by 2013leaver

quick question, Why is CDCl3 used in NMR?

It's a solvent - it carries the molecule in. The Deuterium is used so that a peak/signal is not produced for the CDCl3 on the spectrum.

Reply 1841

Nuna

help...I really don't understand the mark scheme for Q4ai and 4aii on the January 2011 paper??

(edited 10 years ago)

Reply 1842

Tomatochuckers

Anyone know how to go about the Mass spec questions

I know what procedure you need to undertake- but don't know how you can just work out exactly what fragment is responsible for what peak?

Reply 1843

rosie66

Hello
I am really struggling with hydrogen NMR, like i can get what all the peaks are and what they are next to but the only help i can find on the internet has the ratio's on. What i dont get is how do you know how many hydrogens are in the environment when you have no ratios?

Reply 1844

kimsiclez

Original post by rosie66

Original post by Tomatochuckers

Anyone know how to go about the Mass spec questions

I know what procedure you need to undertake- but don't know how you can just work out exactly what fragment is responsible for what peak?

Posted this a few pages back, really helpful in explaining NMR:

Spoiler

Reply 1845

rosie66

Original post by kimsiclez

Posted this a few pages back, really helpful in explaining NMR:

Spoiler

thank you! this guy is really good; better than my teachers

Reply 1846

Jamie66

Hi, can anyone explain why, when using an alkane stationary phase, an alkane will have a longer retention time than an alcohol? It's in the Jan 2012 paper (question 4b) and I can't really work out why it's the case (and the markscheme doesn't really explain it either :frown:

)

Thanks! :biggrin:

Reply 1847

Aikta_S

Original post by Jamie66

)

Thanks! :biggrin:

oooh I did that paper too! isn't it something to do with the hydrogen bonding that the alcohols can do? this probably isn't very helpful... :colondollar:

Reply 1848

Sarangtaec

Original post by Jamie66

)

Thanks! :biggrin:

I think it's because an alkane is a non-polar molecule while an alcohol is polar? But that's confusing cause I would've thought the polar molecule would be more soluble therefore have a longer retention time? lol sorry I don't really know Dx

Or maybe cause non-polar alkane with non-polar alkane would dissolve more onto the stationary phase?
Sorry if I just confused you >_<

Reply 1849

thers

Original post by Jamie66

)

Thanks! :biggrin:

Ask it on the chemistry study help forum. I was going to make a thread later today asking about this but you might aswell create it now.

Reply 1850

Sly1

This is my first time doing F324 and hitting around 39-44 marks on every exam paper.

Reply 1851

D4rth

Original post by Jamie66

)

Thanks! :biggrin:

Like dissolves like.

So since the alkane is non-polar, another non-polar substance will be more soluble in it. The alcohol is polar so it is not as soluble in the stationary phase, the mobile phase carries it through the column much faster, hence it has a shorter retention time. The alkane spends more time in the stationary phase so it takes longer for it to travel and exit the column.

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Reply 1852

exammms!

Hi everyone, please can someone link me to the jan 2013 paper? Thanks :smile:

also, does anyone know an easy way of predicting the number of Carbon NMR peaks of a compound? I always seem to get half the amount of peaks there is and can't understand why! Thank you :smile:

Reply 1853

N.1995

Has anyone got the January 2013 F324 paper PLEASEEEE!!!!?

:redface:

Reply 1854

wl1

Original post by Raj Kang

The splitting patterns would be going top to bottom. Ch3 has no adjacent protons so singlet. Ch2 has 2 adjacent protons so triplet. Ch2 has 3 adjacent protons so quartet. Ch has 2 adjacent protons so splitting of triplet and finally cooh has no adjacent protons so singlet

I still can't get my head around NMR. Why exactly is the splitting pattern for the amine group a singlet? Was it filled in for us because it was an exception? I'm also a bit confused about what exactly the book means by the adjacent carbon. Am I right in assuming if a proton is attached directly to a carbon it means the carbon(s) adjacent to that carbon, and if the proton is on an attached functional group, it means the carbon the functional group is attached to?

Reply 1855

Aikta_S

tada

F324_MS_Jan13.pdf275.0KB

F324-01Jan13.pdf234.6KB

Reply 1856

Sly1

How can I get an A grade in this exam? Just by doing past papers or is there a magic trick?

Reply 1857

D4rth

Original post by Sly1

How can I get an A grade in this exam? Just by doing past papers or is there a magic trick?

Well you've got 21 hours remaining. Ideally you should've completed all the past papers.
I would read over the specification, if there is something you don't know go and learn it quickly.

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Reply 1858

thers

Anyone want to revise?

Reply 1859

Raj Kang

Original post by wl1

For nh2 and oh groups these are singlets because they have no adjacent protons by the n+1 rule. Splitting can only occur on adjacent protons, so the next carbon which has protons attached. If no protons are on adjacent carbons on ether side then that specific type of proton is going to be a singlet