[DoctorDomo]

Can the overhauser nuclear effect occur between two ortho protons attached to a benzene ring, or is the interatomic distance too great? If it occurs but not very commonly, what factors influence that? For example, I reckon its directly proportional to the dishielding on the proton, so would highly deshielded protons (I don't know, maybe the aromatic ring is an electron deficient pyridine ring with a few flourines attached). That brings another question to mind. Do 19F-19F overhauser effects occur, or are th 19F nuclei too shielded with electron density for that?

[Corribus]

Not my area of expertise by any means, but ortho position is not too far, I believe, to see NOE. NOE decreases with 6th power of distance, but I know coupling has been observed farther away than this. Ring currents can be great mediators of spin coupling, too, although how this specifically affects NOE magnitude I do not know. I am sure there is plenty of literature out there on the subject.

Regarding, 19F NOE. Yes, they occur: http://u-of-o-nmr-facility.blogspot.com/2012/11/19-f-noesy.html

[DoctorDomo]

Highly informative answer, thanks a lot! Since phenol is a stronger acid than cyclohexanol, and aniline a weaker base than cyclohexamine, I assume that aromatic ring reduce the electron density on substituents, so I'm guessing that means they should enhance NOE effects because the more bare the proton is (or nucleus for heteroatoms), the stronger the proton-proton interactions should be.

[Ale985]

In my experience, I can say it's difficult to observe a real NOE effect between two protons which are coupling themselves....
If you record a NOE spectrum, you could se a NOE signal...but it derives from magnitude transfer in the coupling.

You can figure out this problem rercording the NOE spectrum two times.
At the first attempt, you set a mixing time = 0 ms
At the second attempt, you set a suitable mixing time for your molecule and solvent (for example 500 ms).
Which is the different?

If you see a signal in the first attempt (mixing time = 0), it's an artefact for sure...because NOE signal can't generate itself in this so short time.
Therefore...you shouldn't see any signals at mixing time = 0...the first attempt is done for check the presence of possible artefact signals...and base line must be clean in the zone you expect your NOE signal.

Once you've figured out it...you can run your NOE experiment

[Babcock_Hall]

Highly informative answer, thanks a lot! Since phenol is a stronger acid than cyclohexanol, and aniline a weaker base than cyclohexamine, I assume that aromatic ring reduce the electron density on substituents, so I'm guessing that means they should enhance NOE effects because the more bare the proton is (or nucleus for heteroatoms), the stronger the proton-proton interactions should be.

I would not expect to see any correlation between electron density and NOE effect.  With respect to the original question, there are both transient and steady-state NOEs observed between adjacent hydrogen atoms (4 and 5) in 3-methylthiophene-2-carboxylic acid, which is a 5- membered aromatic heterocycle.  See p. 129 in "The NOE effect in structural and conformational analysis" by Neuhaus and Williamson (1989).

[Irlanur]

Ring currents can be great mediators of spin coupling, too

NOE is mediated through dipole-dipole coupling.