Downfield isnt low field .... or is it?

[Miffymycat]

In CW or FT pmr, as chemical shift increases, why do we say "downfield" implying a lower magnetic field strength, when deshielded protons need a higher flip energy requiring a higher magnetic field strength and / or higher radio frequency radiation? Am I having a senior moment - apologies if so ...

 

[Borek]

Isn't it the same question that was just asked here: https://www.physicsforums.com/threads/nmr-spectroscopy-question.866769/ ?

 

[Miffymycat]

No - it's a different question. I understand that the energy gap increases with deshielding : my query is I am missing the point as to why we say downfield implying a weaker field if the larger gap needs a stronger applied field?!

 

[DrDu]

You are right, this is quite confusing. I think the field in down- or upfield refers to the induced (or better influenced) field of the shielding electrons.
http://www.foothill.edu/attach/1578/Chapter_14_NMR_Pt._2.pdf

 

[Miffymycat]

Thanks Dr Du yes this makes more sense. I hope there are others who would agree with this to provide confirmation / reassurance!

 

[Mike H]

Upfield/downfield is a relic of the CW NMR era, and should be banished into the abyss when it comes to discussing NMR nowadays. The IUPAC even agrees. It's just confusing, as it's juxtaposed with the shielding/deshielding discussion, which is the important thing to be clear about when discussing chemical shifts.