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

seen at 1614 cm -1 in III-3 and has essentially not changed from III-1, measured to be
1616 cm -1 which is within the maximum resolution of the method. It should be noted
however that aromatic C-C vibrations are also in this region making it difficult to say
with certainty that this is from the carbonyl vibration. The lower frequency for the ester
carbonyl is consistent with the presence of the electron donating methyl substituent
directly adjacent to the C=O carbon. Conversely, the carbonyl stretching frequency is
affected by the electron withdrawing ester directly adjacent to it, as well as the nitrogen
atom from the dithiazyl ring which is four positions away from the C=O carbon, which
both result in a comparatively shorter C-O bond distance and therefore a higher energy
stretch.
Figure 3-2. IR transmission spectra for III-1 and III-3 with labelled peaks in the carbonyl region.
The other peaks in the two spectra are quite similar as the structure has not been
altered dramatically in the other portions of the molecule. Some of the peaks have been
shifted slightly and this is consistent with the different electronic properties of the new
group which has been substituted on the oxygen atom.
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