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

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Discussion Overview

The discussion revolves around the terminology used in NMR spectroscopy, specifically the terms "downfield" and "upfield" in relation to chemical shifts and magnetic field strength. Participants explore the implications of these terms in the context of shielding and deshielding of protons, and the associated energy requirements for resonance.

Discussion Character

  • Debate/contested, Conceptual clarification

Main Points Raised

  • One participant questions why "downfield" is used to imply a lower magnetic field strength when deshielded protons require a higher magnetic field strength for resonance.
  • Another participant suggests that the terms relate to the induced field of shielding electrons rather than the applied magnetic field strength.
  • A different viewpoint posits that the terminology is outdated and should be reconsidered in modern discussions of NMR, as it can lead to confusion regarding the concepts of shielding and deshielding.
  • One participant expresses a desire for confirmation or reassurance regarding the clarification provided by another participant.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness and clarity of the terms "downfield" and "upfield," indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants acknowledge the complexity of the relationship between chemical shifts, shielding, and magnetic field strength, but do not resolve the underlying assumptions or definitions that contribute to the confusion.

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

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