Yatayyat
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Attachment 788528



Attachment 788534


Can anyone please help me how I would answer this question?


What I have tried is that I know that the bottom carbon spectrum would definitely be isomer Q since this is the only one that has 5 peaks and isomer Q is the only one with 5 different carbon environments, so isomer Q goes along with the bottom carbon spectrum.

The trouble is that I'm not quite too sure what the the remaining top two spectra to be? I know that these 2 spectra have only 4 peaks and isomer S and R are the only compounds in which have 4 different carbon environments, hence the top 2 spectra either have to be isomer R and isomer S.

But I'm not sure how to really distinguish between the 2 compounds really. I tried using the carbon nmr data sheet. But that hasn't really helped.

So then how would I do this? Does it have something to do with how shielded one carbon is to the other which depends on what other atoms they are bonded to?
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2nd attachment with spectra broken
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Yatayyat
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(Original post by BobbJo)
2nd attachment with spectra broken
Give me a second, let me repost it.
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(Original post by BobbJo)
2nd attachment with spectra broken
Can you see it now?
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(Original post by Yatayyat)
Give me a second, let me repost it.
I see it now
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(Original post by Yatayyat)
Can you see it now?
[RSQ is what I got]

Agree with Q being third

Peak at 180 means carboxyl
Peak at 25 is alkyl probably
Peak at 50 is sp3 next to oxygen C-O-CO

Q is second because sp3 next to carboxyl/carbonyl at 25-50

ester carbonyl would produce a peak at 190-220

R would be first due to 4 C environments and because that's what is left

not fully sure but hope this helps
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Yatayyat
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(Original post by BobbJo)
[RSQ is what I got]

Agree with Q being third

Peak at 180 means carboxyl
Peak at 25 is alkyl probably
Peak at 50 is sp3 next to oxygen C-O-CO

Q is second because sp3 next to carboxyl/carbonyl at 25-50

ester carbonyl would produce a peak at 190-220

R would be first due to 4 C environments and because that's what is left

not fully sure but hope this helps
I've checked the MS and it says the order to be 'SRQ'.

I get that you can find what functional groups are present in the spectra by looking at the position of the peak. But I find the top two spectra are strikingly similar in terms where some of the peaks are positioned at?

What did you exactly mean when you said 'sp3'?
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(Original post by Yatayyat)
I've checked the MS and it says the order to be 'SRQ'.

I get that you can find what functional groups are present in the spectra by looking at the position of the peak. But I find the top two spectra are strikingly similar in terms where some of the peaks are positioned at?

What did you exactly mean when you said 'sp3'?
sp3 is sp3 hybridised

difference between 1st and 2nd spectra is only in the <50 region

1st spectrum: 40 is carbonyl so C=O hence S

is the evidence I see for S giving the first spectrum
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Yatayyat
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(Original post by BobbJo)
sp3 is sp3 hybridised

difference between 1st and 2nd spectra is only in the <50 region

1st spectrum: 40 is carbonyl so C=O hence S

is the evidence I see for S giving the first spectrum
Oh I see, I've never heard of that term before. Would you mind telling me what 'sp3 hybridised' means in terms of what actually happens in terms of electronegativity and shielding.

Would you have had to know that in order to answer this question?
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Yatayyat
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(Original post by BobbJo)
sp3 is sp3 hybridised

difference between 1st and 2nd spectra is only in the <50 region

1st spectrum: 40 is carbonyl so C=O hence S

is the evidence I see for S giving the first spectrum
But doesn't both R and S have the carbonyl group in them. Why isn't that I couldn't have just let isomer R to be placed as the first spectrum?
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(Original post by Yatayyat)
Oh I see, I've never heard of that term before. Would you mind telling me what 'sp3 hybridised' means in terms of what actually happens in terms of electronegativity and shielding.

Would you have had to know that in order to answer this question?
No.

Hybridisation is the process of "mixing orbitals".
e.g Carbon is 1s2 2s2 2p2. It has only 1 unpaired electron and can only form 1 bond.
But in reality carbon forms 4 bonds. This is rationalised as follows
Electrons are promoted to empty p orbitals
the s and 3 p orbitals "mix" to produce 4 identical sp3 orbitals. An sp3 orbital has 75% p character and 25% character. Energy is required for promotion of electron to empty orbital. But this allows carbon to form 4 bonds. The energy released during bond forming compensates for this.
Also, s orbitals are smaller than p orbitals. So bond lengths and strengths would be uneven. (methane CH4 would be a distorted tetrahedron). X-ray crystallography showed that they are all identical. This proves all bonds are the same. In fact all bonds in methane are formed by sp3-s overlap. There must have been hybridisation.
Lastly, sp3 orbitals are degenerate

Not required to answer this question
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(Original post by Yatayyat)
But doesn't both R and S have the carbonyl group in them. Why isn't that I couldn't have just let isomer R to be placed as the first spectrum?
yes that group is 190-220

it is the carbon next to the carbonyl

i'm not sure your data booklet is the same as mine

this topic is quite difficult

im using this
https://www.cambridgeinternational.o...ta-booklet.pdf
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Yatayyat
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(Original post by BobbJo)
yes that group is 190-220

it is the carbon next to the carbonyl

i'm not sure your data booklet is the same as mine

this topic is quite difficult

im using this
https://www.cambridgeinternational.o...ta-booklet.pdf
I'm using the AQA exam data sheet, since this is the only one I'm required to use.

I find it quite troubling to interpret the spectrum most of the time since a lot of the functional group clashes with others in terms where the range lies. It doesn't give us any info about the sp3 as well.


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(Original post by Yatayyat)
I'm using the AQA exam data sheet, since this is the only one I'm required to use.

I find it quite troubling to interpret the spectrum most of the time since a lot of the functional group clashes with others in terms where the range lies


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Seems similar to mine

I do agree with you that it is a troublesome topic. NMR is decidedly a powerful tool though

Anyway, I believe the peak at 40 is due to the 3rd type of carbon in table C
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Yatayyat
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(Original post by BobbJo)
Seems similar to mine

I do agree with you that it is a troublesome topic. NMR is decidedly a powerful tool though

Anyway, I believe the peak at 40 is due to the 3rd type of carbon in table C
Okay, I guess the key difference was only to look out for the region that was <50 as you mentioned before. I'll try not to complicate anymore as it already is. But thank you so much for you help too
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