1,2,3-Dithiazolyl and 1,2,35-Dithiadiazolyl Radicals as Spin-Bearing ...

1.1.2 Electronic Considerations
A useful tool for examining radical molecules is EPR spectroscopy as it permits for
the environment of an unpaired electron to be probed by determining nuclear spins of the
atomic nuclei with which it is most closely associated, providing some insight with
respect to the identity of the nucleus. The unpaired electron resides in a singly occupied
molecular orbital (SOMO) which may be delocalized over several atomic nuclei,
however atoms which do not have a SOMO coefficient can still be detected via EPR
through a phenomenon known as spin polarization.
Spin polarization occurs due to fact that an unpaired electron in a SOMO creates a
magnetic field which will affect the relative energies of underlying electron pairs. The
result is that electrons which possess the same spin orientation as the unpaired electron in
the SOMO (designated α spin) will be lower in energy than the opposite spin orientation
(designated β spin). This occurs because the spatial component of the orbital Ψ will be
different for the two possible m s quantum values. This essentially lowers the coulombic
repulsion of the paired electrons with one another and enhances the exchange energy of
the two electrons with α spin. The overall effect is that atoms within a molecular radical
system which do not have a coefficient of the singly occupied molecular orbital may still
possess radical character.
While the systems of interest in this thesis have spins which are delocalized over
several atoms, the concept of spin polarization can be illustrated succinctly by
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