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N,N,N-Tris[p-(N-oxyl-tert-butylamino)phenyl]amine (N) was obtained as dark violet plates by lithiation of tris(4-bromophenyl)amine, followed by reaction with 2-methyl-2-nitrosopropane and oxidation of the resulting tris(hydroxyamine) with Ag 2 O. An X-ray crystal and molecular structure analysis of the monoclinic single crystal with space group Cc showed that it has neither C 3 symmetry nor zwitterionic quinonoid structure. An EPR spectrum in MTHF solution at room temperature consisted of seven lines (a N ) 4.06 G (3N) at g ) 2.0058). The temperature dependence of the magnetic susceptibility data on N in the range 2-300 K was analyzed in terms of a triangular coupling model for three S ) 1/2 spins to give a set of best-fit parameters which placed a doublet state as the ground state with a quartet state lying 559 K () 1.11 kcal mol -1 ) above it. B3LYP/6-31G*//B3LYP/6-31G computations were performed on both spin states of a model molecule (N′) in which all three N-tert-butyl groups in N were replaced with N-methyl groups. The doublet state was found to be more stable than the quartet state by 0.84 kcal mol -1 . Tris[p-(N-oxyl-tert-butylamino)phenyl]methyl (C) gave a monoclinic single crystal with space group Cc (no. 9) and has been shown to have a benzoquinoneimine N-oxide type diradical structure. Temperature dependence of its magnetic susceptibility showed that C has a triplet ground state with a singlet state lying 410 K above the triplet. Reactions of the corresponding organolithium compounds with BF 3 ‚OEt 2 were not applicable to give tris[4-(N-oxyl-tert-butylamino)phenyl]borane (B) but its 2,2′,2′′,6,6′,6′′-hexamethyl derivative (B′). In the trigonal crystal with space group R 3 h (no. 148), the three benzene rings are tilted by 49.2°with respect to the valence plane of the boron atom. The magnetic susceptibility data on B′ were consistent with a doublet ground state with an energy gap to a quartet state by 9.9 K () 0.0197 kcal mol -1 ). All the results together with ab initio MO studies are consistent with a picture that the ground spin states of title compounds N, C, and B are doublet, triplet, and doublet, respectively. The electronic structures are explained qualitatively by p-(N-oxyl-tert-butylamino)phenyl homologues of (•H 2 C) 3 X in which X ) N, C‚, and B atoms, and two, one, and no π-electrons are contained, respectively.