Lighfy
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Hey,

Struggling a bit with proton NMR. I was wondering if anyone could explain could help me out with this conundrum I've got

On page 103 of the OCR A2 textbook it asks to deduce the structure of an unknown compound with the molecular formula C9H10O. I understand everything apart from the splitting pattern the NMR spectrum provides.

From chemical shift values of 7.0-7.9, there are two doublet peaks which means that the benzene molecule is adjacent to 1 hydrogen atom (X2 as there are 2 peaks). I can't figure out why the splitting pattern is like this when I look at the overall molecule.

The structure of the molecule is a benzene molecule bonded to CH3CH2- on carbon 1, and CHO on carbon 4?

Can anyone explain to me why there are two doublet peaks?

Thanks.
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charco
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(Original post by Lighfy)
Hey,

Struggling a bit with proton NMR. I was wondering if anyone could explain could help me out with this conundrum I've got

On page 103 of the OCR A2 textbook it asks to deduce the structure of an unknown compound with the molecular formula C9H10O. I understand everything apart from the splitting pattern the NMR spectrum provides.

From chemical shift values of 7.0-7.9, there are two doublet peaks which means that the benzene molecule is adjacent to 1 hydrogen atom (X2 as there are 2 peaks). I can't figure out why the splitting pattern is like this when I look at the overall molecule.

The structure of the molecule is a benzene molecule bonded to CH3CH2- on carbon 1, and CHO on carbon 4?

Can anyone explain to me why there are two doublet peaks?

Thanks.
There are two pairs of equivalent protons on the benzene ring itself, the protons in the 2,6 positions and the protons in the 3,5 positions. These split each other.

The benzene protons are not split by attachments to the ring as any hydrogens would have to be at least two steps away from the ring hydrogens.
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Pigster
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The OCR A spec. says:

"Candidates will be expected to identify aromatic protons from chemical shift values but will not be expected to analyse their splitting patterns"

i.e. you would be expected to recognise the shift values as being benzene environment H's, but not explain the splitting patterns.
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Lighfy
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(Original post by charco)
There are two pairs of equivalent protons on the benzene ring itself, the protons in the 2,6 positions and the protons in the 3,5 positions. These split each other.

The benzene protons are not split by attachments to the ring as any hydrogens would have to be at least two steps away from the ring hydrogens.
Ahhh I see, thank you!
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