Dibromonitroso benzene sulphonate spin-adducts — Why no hyperfine coupling to bromine?

Abstract

Both ⁷⁹Br and ⁸¹Br nuclei have very large magnetic moments and hence can give rise to large hyperfine splittings. However, for the title compound, dibromonitroso-p-benzene sulphonate (DBNBS), which is a widely used spin-trap, liquid-phase spectra of radical adducts are characterised by narrow EPR features with no bromine splitting, despite the expected delocalisation of spin-density onto bromine. I find that for such radicals in the solid-state the ¹⁴N parallel features are very broad, although the seven expected hyperfine features from the ⁷⁹Br and ⁸¹Br nuclei were not clearly defined. I use these results to offer an explanation for the complete absence of any hyperfine splitting from bromine in the isotropic spectra.

Keywords:

• Bromine
• EPR
• free radicals
• spin-trap
• nitroxyl radicals