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

electron density on the two, more electronegative, nitrogen atoms and is therefore more
thermodynamically stable than I-15.
When R = CH 3 , t Bu or Ph it was found that the rearrangement was photoinduced,
whereas for more electronegative substituents such as R = CF 3 or 3,5-(NO 2 )C 3 H 3 the
rearrangement could take place in the absence of light, although at a much slower rate. 67
It was found that the rearrangement for these compounds at a given concentration was
positively correlated to the electronegativity of the substituent R group. 71
This
rearrangement was found to be second order with respect the radical concentration (for R
= CH 3 ) via the half-life method using EPR spectroscopy 72 and was proposed to proceed
via the formation of a π*- π* dimer shown in Figure 1-6. Following the necessary
rearrangement of atoms, the 1,2,3,5-DTDA based dimer is formed.
Figure 1-7. Dimerization and proposed rearrangement pathway for conversion of I-15 to I-16.
As mentioned previously, the SOMO for I-16 based radicals resembles π 4 from
Figure 1-4 in that it has no coefficient on the carbon atom of the DTDA ring. 70,73 The
only spin density in this position is β spin and comes from spin polarization. This means
that the R group can be tailored to suit a variety of functions with no impact on the first
order electronic structure of the radical. However, as the majority of the spin density is on
the sulfur and nitrogen atoms of the 1,2,3,5-DTDA ring, these compounds are prone to
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