Hydrogen Environments in o-Toluic Acid?

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Discussion Overview

The discussion revolves around the analysis of hydrogen environments in o-Toluic acid as observed through NMR spectroscopy. Participants are exploring the discrepancies in reported hydrogen environments between different NMR solvents and databases.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant initially identifies four hydrogen environments in o-Toluic acid but finds conflicting information in databases, with one NMR indicating five environments and another indicating four.
  • Another participant proposes that there are actually six different hydrogen environments, suggesting that two environments may have similar shifts.
  • A participant questions why certain hydrogen environments, specifically those on carbons 4 and 5, would not be considered the same due to their adjacency.
  • A later reply emphasizes that in aromatic systems, the lack of symmetry and varying electron density due to functional groups leads to different hydrogen environments, not just proximity to other atoms.

Areas of Agreement / Disagreement

Participants express differing views on the number of hydrogen environments present in o-Toluic acid, with no consensus reached on the correct count or the reasoning behind the observed discrepancies.

Contextual Notes

The discussion highlights the complexity of hydrogen environments in aromatic compounds and the influence of molecular symmetry and functional groups on NMR results. Specific assumptions about hydrogen environments based on adjacency are challenged.

AXidenT
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Hi, I'm doing a spectroscopy assignment and am analysing the NMR for p-Toluic acid. However, I need to understand the NMRs of it's isomer o-Toluic acid as well.
http://en.wikipedia.org/wiki/O-toluic_acid
On first inspection, I thought there was 4 Hydrogen environments present in this molecule, yet I have found some databases stating otherwise?

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

If you search "o-Toluic acid" and go to the top result both NMRs disagree with what I'd think to be correct. The CDCl3 Hydrogen NMR states that there is 5 hydrogen environments, whilst the DMSO-d6 Hydrogen NMR states there is 4 hydrogen environments, yet it labels two non-adjacent Hydrogens with different environments as the same.

As a result can anyone help me figure out how many hydrogen environments are present in o-Toluic acid and which are which? Help greatly appreciated! Thank you!
 
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I would say there are six different environments, of which two happen (more or less accidentally) to have the same shift.
 
Ah that'd make things easier for me. :P

Why would that be exactly though? I would have thought the hydrogens off carbons 4 and 5 (counting clockwise around the aromatic ring from the COOH carbon) would have been the same environment since on the adjacent atoms are the same?

Thank you! :D
 
You have been already answered at CF - not only the closest atoms count. Especially in the case of aromatic system lack of symmetry means different environments, as electron density in different places of the ring depends on the functional groups.