The electronic structure of 2-methoxy-1,3,5-benzenetriyltris (N-hydron
itroxide) (MBTN) is discussed with the ab initio molecular orbital met
hod at the second-order Moller-Plesset perturbation level of theory. T
he result explains why high-spin states are unstable in some hindered
nitroxide di- and triradicals coupled through m-phenylene.