著者

Ishigaki Yusuke Shimajiri Takuya Takeda Takashi Katoono Ryo Suzuki Takanori

雑誌

Chem (ISSN:24519294)

巻号頁・発行日

vol.4, no.4, pp.795-806, 2018-04-12

被引用文献数

93

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On the basis of the intramolecular “core-shell strategy,” we designed dihydropyracylene with two spiro(dibenzocycloheptatriene) units, for which theoretical calculations predicted a very weak C–C bond with a bond length around 1.8 Å. This bond is expanded by the forced adoption of an eclipsed conformation and by angle strain through a “scissor effect.” The highly strained hydrocarbon was isolated as a thermally stable compound with no signs of diradical contribution because the weak C–C bond (core) is protected by the shape-persistent fused-ring structure (shell). A Raman shift corresponding to the C–C stretching vibration (587 cm−1) was very different from that for ethane (993 cm−1). The bond length determined by X-ray (1.806(2) Å) was greater than the shortest non-bonded intramolecular C…C contact (1.80(2) Å). The assumed limit for a C–C bond (1.803 Å) by supposing linear correlation between bond length and bond-dissociation energy for covalent bonding was proven to be invalid.