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Author: Subject: H-NMR Multiplicity of aldehyde hydrogen on 3-fluorobenzaldehyde
thors.lab
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[*] posted on 4-10-2020 at 21:26
H-NMR Multiplicity of aldehyde hydrogen on 3-fluorobenzaldehyde

So I would suspect the aldehyde hydrogen on 3-fluorobenzaldehyde to be a singlet right? The adjacent carbon has no hydrogens attached. But the ChemAxon chemicalize calculator says that would be a triplet:




Why? Is this something to do with the conjugated system?



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DraconicAcid
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[*] posted on 4-10-2020 at 22:55


Yes, you can sometimes get what is called "W-coupling".



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[*] posted on 5-10-2020 at 06:42


Quote: Originally posted by DraconicAcid  
Yes, you can sometimes get what is called "W-coupling".


Awesome, thank you!



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AvBaeyer
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[*] posted on 5-10-2020 at 18:10


The multiplicity is a result of long distance coupling with the fluorine atom. H-F couplings occur through several bonds. Any good NMR text will give you an explanation with examples.

AvB
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[*] posted on 5-10-2020 at 18:28


Quote: Originally posted by AvBaeyer  
The multiplicity is a result of long distance coupling with the fluorine atom. H-F couplings occur through several bonds. Any good NMR text will give you an explanation with examples.

AvB


No, because it's a triplet. If it was coupling to the F, it would be a doublet.



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[*] posted on 6-10-2020 at 10:03


W coupling would be 4J, in this example it is 5J. So no W coupling. Also in reality it is a doublet, see attachment, so I second avbaeyer. Source:Sigma aldrich

Attachment: FNMR010527.PDF (99kB)
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