Sciencemadness Discussion Board

H-NMR Multiplicity of aldehyde hydrogen on 3-fluorobenzaldehyde

thors.lab - 4-10-2020 at 21:26

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?

DraconicAcid - 4-10-2020 at 22:55

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

thors.lab - 5-10-2020 at 06:42

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


Awesome, thank you!

AvBaeyer - 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

DraconicAcid - 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.

Sigmatropic - 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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