[AXidenT]

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!

[DrCMS]

What do you think and why?

[AXidenT]

I thought 5 because the hydrogens off carbons 4 and 5 (counting clockwise around the aromatic from the COOH carbon) had the same environment - like all the adjacent atoms are the same I thought? However both the sources in the database suggest otherwise. :S

[fledarmus]

The database is not describing different hydrogen environments, it is describing different peaks in the NMR. There is no rule that says that different hydrogen environments can't coincidentally give the same chemical shift in the NMR spectrum. The use of different solvents or salts may allow you to differentiate between hydrogens that happen to have the same chemical shift and hydrogens that are actually in the same chemical environment.

[DrCMS]

No the hydrogens on those carbons in o-Toluic acid are in very similar environments but they not identical.  

o-Toluic acid has 6 different hydrogens while p-Toluic acid only has 4 because it is symmetrical.

[AXidenT]

Aaahh I think I have previously misunderstood how to locate and identify hydrogen environments. So, does this mean that if you had two identical functional groups on different parts of a large, non-symmetrical molecule, they would be different hydrogen environments? I was under the impression it was only determined by the number of hydrogens in different hydrogen environments on adjacent atoms (typically carbon). Perhaps that was a simplified explanation.

Thank you! I actually think I'm getting a better understanding of this all now.