ESR Studies of a New Stable π-Conjugated 4,4′-(Biphenyl-3,3′-diyl)bis(aryloxyl) Biradical

ENDOR observations were carried out for 2,6-di-t-butyl-4-phenylphenoxyl and some of its derivatives. Based on the proton hyperfine splittings, the structure of the aryloxyl monoradicals was investigated in terms of the McLachlan MO calculation. A new stable π-conjugated bis(aryloxyl) biradical, 4,4′-(biphenyl-3,3′-diyl)bis(2,6-di-t-butylphenoxyl), was prepared, and the g- and D-tensor values of the biradical in toluene have been determined from its asymmetric frozen ESR spectrum. The D-tensor values were calculated for the twisted “cis” and “trans” conformers of the biradical molecule, using the McLachlan spin densities of 2,6-di-t-butyl-4-phenylphenoxyl, which is a monoradical half of the biradical.