[celesfr]

How can I tell in NMR the difference between Ortho, Meta and Para hidrogens??
My particular case is this molecule:

CH2=CH-O-C(=O)- "RING" -O-CH-(CH3)2

and the signals for the aromatic are these:
6,90ppm  (d, 1H)
7,95ppm  (dd,1H)
7,85ppm  (d, 2H)

Is there any rule that applies to all cases??

thanks!

[Markovnikov]

The J-coupling constant between ortho, meta and para hydrogens are different. Depending on the strength of the NMR-machine you may be able to separate the peaks or not.

Usually the para-coupling constant cannot be seen, but for an example a hydrogen coupling to one ortho hydrogen and two meta hydrogens would give a doublet of triplets, since J-coupling constant for ortho hydrogens is larger than meta hydrogens. This way you can figure out how your substituents are positioned.