Hydrogen Environments in o-Toluic Acid?

[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!

 

[Borek]

I would say there are six different environments, of which two happen (more or less accidentally) to have the same shift.

 

[AXidenT]

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]

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.

 

[LudusRex]

I would first like to commend you for your thorough analysis and research on o-Toluic acid. It is important to question and verify information in order to have a clear understanding of the topic at hand.

After reviewing the available information, I can confirm that there are indeed 5 hydrogen environments in o-Toluic acid. This is due to the presence of a carboxylic acid group (-COOH) which can exhibit different chemical shifts in different solvents. The CDCl3 NMR spectrum shows the chemical shifts for the hydrogens in the presence of the solvent chloroform, while the DMSO-d6 NMR spectrum shows the chemical shifts in the presence of dimethyl sulfoxide.

In order to determine which hydrogen environments correspond to which hydrogens, it is important to consider the molecular structure of o-Toluic acid. The carboxylic acid group has two hydrogens (H1 and H2) attached to the carbon atom, and these two hydrogens would exhibit the same chemical shift in both solvents. The next two hydrogens (H3 and H4) are attached to the benzene ring and would also exhibit the same chemical shift in both solvents. The fifth hydrogen (H5) is attached to the carbon atom adjacent to the carboxylic acid group and would exhibit a different chemical shift in each solvent.

Therefore, the CDCl3 NMR spectrum is labeling H1 and H2 as one environment, H3 and H4 as another environment, and H5 as a third environment. The DMSO-d6 NMR spectrum is labeling H1 and H2 as one environment, H3 and H4 as another environment, and H5 as the same environment as H3 and H4 due to the different chemical environment created by the solvent.

In conclusion, o-Toluic acid has 5 hydrogen environments due to the presence of a carboxylic acid group, and the discrepancies in the NMR spectra can be attributed to the different chemical environments created by the solvents used. I hope this helps clarify any confusion and aids in your spectroscopy assignment. Best of luck!