Knowledge Bank

The two $CF3$ groups of the neutral 4,5-bis(trifluoromethy)-1,3,2-dithiazolyl radical are large enough to inhibit free rotation along their C-C axes. The energy barrier due to these rotations is $\approx 60$ kcal/mol. Consequently, the six $\mathrm{<mrow\; data-mjx-texclass="ORD">19</mrow>}F$ atoms are expected to be magnetically inequivalent in the solid state. This is verified from the electron paramagnetic resonance (EPR) of the radical in solution and in an Ar matrix. At room temperature the radical-radical exchange broadening inhibits the observation of $\mathrm{<mrow\; data-mjx-texclass="ORD">19</mrow>}F$ superhyperfine interaction. As the temperature is lowered the rate of radical-radical encounter decreases and the isotropic $\mathrm{<mrow\; data-mjx-texclass="ORD">19</mrow>}F$ superhyperfine splittings are well resoved. In an Ar matrix, when the radical and its $CF3$ are prohibited from rotation, the inhomogenous broadening due to magnetic inequivalency is so strong that even the $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$ hyperfine splittings are masked. A detailed theoretical derivation of the $\mathrm{<mrow\; data-mjx-texclass="ORD">19</mrow>}F$ superhyperfine tensors in terms of the molecular orbital coefficients is presented and used to simulate the solid state EPR spectrum.