OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

Reply 1060

tcameron

19

Original post by rory58824

So the spltting patterns only include protons on adjacent CARBON atoms, not adjacent nitrogen or oxygen atoms?

Yeah it isn't to do with nitrogen or oxygen

Reply 1061

underestimate

9

Hi
Just wanted to ask why an -O- bond is not shown at the end of the chain on the left when in other cases it is shown.
And how is a resort unit for a hydroxypropanoic acid drawn?

Reply 1062

rory58824

2

Original post by tcameron

Yeah it isn't to do with nitrogen or oxygen

Thanks, just wanted to clear that up :smile:

Anyone predicting a tough paper tomorrow?

Reply 1063

Noura*

10

Hi guys, can anyone explain where the 2nd oxygen is coming from in this NMR question? In both the H and C diagrams, there is no peak showing the O in the ester but suddenly it appears in the final structure, and yes I saw that in the molecular formula there is supposed to be 2 O's but shouldn't it appear in the NMR diagrams?
Molecular formula is C10H1202

June 13, last question

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Reply 1064

qweening

2

What are the steps for Gas Chromatography (and YES we do need to know this, expected as overall knowledge in the spec)

Reply 1065

RetroSpectro

2

Original post by underestimate

Hi
Just wanted to ask why an -O- bond is not shown at the end of the chain on the left when in other cases it is shown.
And how is a resort unit for a hydroxypropanoic acid drawn?

It could be shown on either side it does not matter as long as a full repeat unit is displayed

Reply 1066

qweening

2

Original post by Noura*

Hi guys, can anyone explain where the 2nd oxygen is coming from in this NMR question? In both the H and C diagrams, there is no peak showing the O in the ester but suddenly it appears in the final structure, and yes I saw that in the molecular formula there is supposed to be 2 O's but shouldn't it appear in the NMR diagrams?
Molecular formula is C10H1202

June 13, last question

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That's because there is no Hydrogens attached so there's no peak, you're expected to deduce that there has to be a =o attached to the benzene as there's a peak for c6h5c-
(and obviously by looking at important peaks on the C spectrum)

(edited 7 years ago)

Reply 1067

M.Branson98

2

Original post by Noura*

Hi guys, can anyone explain where the 2nd oxygen is coming from in this NMR question? In both the H and C diagrams, there is no peak showing the O in the ester but suddenly it appears in the final structure, and yes I saw that in the molecular formula there is supposed to be 2 O's but shouldn't it appear in the NMR diagrams?
Molecular formula is C10H1202

June 13, last question

Attachment not found

If you look at the carbon-13 NMR, there is a peak at about 184ppm which indicates a carbon bonded to two oxygens, one with a double bond and one with a single bond. So this indicates that it's an ester.

Reply 1068

rory58824

2

Original post by Noura*

Hi guys, can anyone explain where the 2nd oxygen is coming from in this NMR question? In both the H and C diagrams, there is no peak showing the O in the ester but suddenly it appears in the final structure, and yes I saw that in the molecular formula there is supposed to be 2 O's but shouldn't it appear in the NMR diagrams?
Molecular formula is C10H1202

June 13, last question

Attachment not found

The structure shows HC-C-O. A peak would be around 3.5-4ppm for HC-O, but that environment is not present in this structure.

Reply 1069

RetroSpectro

2

Can anyone elaborate on what we are expected to know regarding this statement from the Spec:

"describe and explain the increased use of esters of fatty acids as biodiesel."

Reply 1070

Noura*

10

Original post by M.Branson98

If you look at the carbon-13 NMR, there is a peak at about 184ppm which indicates a carbon bonded to two oxygens, one with a double bond and one with a single bond. So this indicates that it's an ester.

Original post by qweening

That's because there is no Hydrogens attached so there's no peak, you're expected to deduce that there has to be a =o attached to the benzene as there's a peak for c6h5c-

Oh rights yes, I get it, but shouldn't it appear in the carbon spec¿

Reply 1071

fruitpastilles

4

You know when you have the polymer of a hydoxy carbonxlic acid (like CH2OHCOOH but with stuff in the middle) if it asks you to draw the repeat unit of the polymer which side do you put the O in the ester link?

Reply 1072

qweening

2

Original post by RetroSpectro

Can anyone elaborate on what we are expected to know regarding this statement from the Spec:

"describe and explain the increased use of esters of fatty acids as biodiesel."

triglycerides + methanol = biodisel + glycerol
naoh catalyst
methanol is excess to increase yield
high atom economy and glycerol is a useful byproduct
biggest thing is that methanol is renewable to used more as it doesn't release co2 or greenhouse gases for better for the environment etc

Reply 1073

tcameron

19

Original post by qweening

What are the steps for Gas Chromatography (and YES we do need to know this, expected as overall knowledge in the spec)

Component is injected into the column and separated through the movement of the mobile phase (an inert gas such as helium)
Inside the column the components seperate by relative solubility if it is a liquid stationary phase on a solid support or adsorption if the stationary phase is a solid.
The components which are most soluble will leave the column last and so have the longest retention time which is the time from injection to detection

Not sure what else is needed?

is this for ocr b?

Original post by Ambre

is this for ocr b?

Nope that's F334 and F335

Reply 1076

M.Branson98

2

Do examiners mark annotated spectra for carbon 13 and proton NMR?

Reply 1077

Serine Soul

18

Original post by M.Branson98

Do examiners mark annotated spectra for carbon 13 and proton NMR?

I think they do

Reply 1078

qweening

2

Original post by tcameron

Component is injected into the column and separated through the movement of the mobile phase (an inert gas such as helium)
Inside the column the components seperate by relative solubility if it is a liquid stationary phase on a solid support or adsorption if the stationary phase is a solid.
The components which are most soluble will leave the column last and so have the longest retention time which is the time from injection to detection

Not sure what else is needed?

Well the spec says:
''Candidates may be expected to interpret provided gas chromatograms and mass spectra'' so I would know (roughly) the steps on page 80 to be safe:

1) Mixture injected into column and vaporised
2) Mobile, inert carrier like n2 flushes mixture down column

And then what you said. But I would also know the diagram on page. 81. Just know that peaks occur on a graph of X axis = TIME and Y axis = Absorption. Also area under peak is equivalent to the amount of the substance