2,7-Di-tert-butyl-9,9′(10H,10′H)-spirobiacridine-10,10′-dioxyl as a ground triplet biradical: The role of tert-butylation

Kana Ichihashi, Takuya Kanetomo, Masaya Enomoto, Takayuki Ishida

Research output: Contribution to journalArticle


The synthesis of a doubly tert-butylated spirobiradical, 2,7-di-tert-butyl-9,9′(10H,10′H)-spirobiacridine-10,10′-dioxyl is reported. The X-ray diffraction study clarified that the two dihydroacridine skeletons were fused at the sp3-carbon atom affording a cruciform structure. The frozen-solution electron spin resonance spectrum showed a typical zero-field-splitting pattern. The magnetic study revealed the presence of an intramolecular ferromagnetic interaction with 2J/kB = +22.3(5) K. The density-functional-theory calculation results are entirely consistent with the experimental results. After comparison with the known unsubstituted spirobiradical, we can conclude that tert-butylation is a useful method to reduce the intermolecular interaction without breaking the degeneracy of the singly occupied molecular orbitals.

Original languageEnglish
Article number152428
JournalTetrahedron Letters
Issue number43
Publication statusPublished - 22 Oct 2020


  • Aminoxyl
  • Biradical
  • High-spin molecule
  • Intermolecular interaction
  • Spiro compound

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