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Published July 1986 | Published
Journal Article Open

Effects of Substituents on the Length of Central C(sp^3)-C(sp^3) Bond in Anthracene Photodimers and Related Molecules

Abstract

Effects of substituents on the lengths of the central C–C single bond in the butterfly-shaped anthracene photodimers (1)–(7) and lepidopterenes (8) are studied. X-Ray analysis of the photodimer (10) of 9,10-difluoroanthracene gave a C(9)–C(10′) bond length of 1.631 (3)Å. An attempt to re-determine molecular structure of the photoisomer (5) of [2.2](9,10) anthracenophane (12) by neutron diffraction analysis is also reported [C(9)–C(10′): obs. 1.64(1), calc. 1.63(1)Å]. The D_2 structure that had been proposed for the minimum-energy conformation of (5) is questioned and the D_(2h) symmetric conformation is suggested on the basis of the diffraction results and MNDO calculations. The experimentally determined distances of the long central C–C bonds in these butterfly compounds including dianthronyl (9) are well reproduced by MNDO calculations with a standard deviation of 0.013 Å. Small but significant further elongation of the central C–C bond by up to 0.07 Å resulting from annulation of cyclobutane or cyclopentane ring in anthracene photodimers and from remote chlorine substitution in lepidopterene are interpreted in terms of the increased π→σ^* orbital interaction.

Additional Information

© 1986 Royal Society of Chemistry. Received 10th June 1985; Paper 5/978. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education at Sapporo and by a Camille and Henry Dreyfus Grant for Newly Appointed Young Faculty in Chemistry at Pasadena. G. K. thanks Dr. W. Littke for technical advice and for making available his microscope facilities. D. A. D. thanks Professor R. E. Marsh for helpful discussions and J. A. Rice, Caltech, for technical assistance. Calculations have been carried out at the Computing Centers of Hokkaido University and the Institute of Molecular Science, and at Caltech on the Theoretical Chemistry Computer funded through grants from the Camille and Henry Dreyfus Foundation, the National Science Foundation, and the Sloan Fund of the California Institute of Technology.

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August 19, 2023
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