[2+2] Cycloaddition Products of Tetradehydrodianthracene: Experimental and Theoretical Proof of Extraordinary Long CC Single Bonds

• Published in: Angewandte Chemie International Edition Vol. 36; no. 16; pp. 1757 - 1760
• Main Authors: Kammermeier, Stefan, Herges, Rainer, Jones, Peter G.
• Format: Journal Article
• Language: English
• Published: Zug Hüthig & Wepf Verlag 01-09-1997
• Subjects: anthracene dimers; cycloadditions; density functional calculations; Raman spectroscopy; strained molecules
• ISSN: 0570-0833; 1521-3773
• DOI: 10.1002/anie.199717571

An extremely long CC single bond of 1.713 Å is found in the [2+2] cycloadduct of ortho‐didehydrobenzene and tetradehydrodianthracene. The force constant of this central bond is reduced to only 30% of that of the CC bond in ethane. The corresponding CC stretching vibration (687 cm−1) in the Raman spectrum is red‐shifted 300 cm−1 relative to the bands of “normal” hydrocarbons.