[spirochete]

I'm trying to teach myself the basics of electron paramagnetic resonance (EPR) spectroscopy and I'm having a tough time digging through the Wikipedia page on it.  There are too many equations and I'm really just looking for a general, mostly qualitative idea of how EPR works and what information an EPR spectrum gives us in a practical sense.  At this point all I know is that when you get a spectrum with wavy lines, this means the solution contains molecules with unpaired electrons.  When you get just a straight line, that means the molecules in solution have all paired electrons.   

To give you an idea of the level of detail I'm looking for, I'll describe NMR in a similar way.  I'm looking for the same type of qualitative description of EPR spectroscopy:

"Certain chemical nuclei (most importantly ¹H and ¹³C) have magnetic properties.  When exposed to a magnetic field, the majority of these nuclei will align themselves with the field.  Absorption of radio waves will cause some of the nuclei to go into a higher energy state where they oppose the magnetic field.  The exact frequency that the nuclei absorb gives us information about the chemical environment of the nuclei.  Nuclei with more electron density around them ("Shielded" nuclei) absorb at a higher frequency and thus appear "upfield" (to the right) on an NMR spectrum."   

Also some general questions I have:

What information does an EPR spectrum give besides Radical/No radical?  IE: Can it tell you the concentration of radical in solution, or the type of radical?

Thanks for reading!

[Cool Doll]

EPR measures the unpaired electron in a similar way that NMR. A magnetic field is applied that align the spin to the field either +1/2 or -1/2. Then you send in and laser pulses which pertubate the electrons and you can see from the relaxation energies which molecules are present and what there surroundings are. g which are a ratio between the electrons different angular moments. µ is the electrons magnetic dipole moment and these differs from molecule to molecule, therefore you can characterize with EPR.

[Babcock_Hall]

Chapter 7 in "Biological Spectroscopy" by Iain D. Campbell and Raymond A Dwek (Benjamin Cummings, 1984) is very well written.