Hydrogen Environments in o-Toluic Acid?


by AXidenT
Tags: acid, environments, hydrogen, otoluic
AXidenT
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#1
Mar28-12, 08:53 AM
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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..._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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Borek
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Mar28-12, 09:13 AM
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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.
AXidenT
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#3
Mar28-12, 09:30 AM
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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

Borek
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Mar28-12, 01:27 PM
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Hydrogen Environments in o-Toluic Acid?


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.


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