A Puckered Singlet Cyclopentane‐1,3‐diyl: Detection of the Third Isomer in Homolysis |
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Authors: | Jianhuai Ye Dr Sayaka Hatano Prof?Dr Manabu Abe Prof?Dr Ryohei Kishi Yusuke Murata Prof?Dr Masayoshi Nakano Prof?Dr Waldemar Adam |
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Institution: | 1. Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), Hiroshima, Japan;2. Research Center for Future Science, Hiroshima University (HIRODAI), Hiroshima, Japan;3. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan;4. Institute of Organic Chemistry, University of Würzburg, Würzburg, Germany;5. Department of Chemistry, Facundo Bueso 110, University of Puerto Rico, Rio Piedras, Puerto Rico, USA |
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Abstract: | In the photochemical denitrogenation of 1,4‐diaryl‐2,3‐diazabicyclo2.2.1]heptane ( AZ6 ) bearing sterically hindered substituents, a curious new absorption band at about 450 nm was observed under low‐temperature matrix conditions, together with the previously well‐characterized planar singlet diradical pl‐1 DR6 with λmax=≈580 nm. The 450 nm species was electron paramagnetic resonance (EPR)‐silent. Instead of generating the planar diradical pl‐1 DR6 and the precursor azoalkane AZ6 upon warming, the ring‐closed bicyclo2.1.0]pentane derivative SB6 , that is, the AZ6 denitrogenation product was identified. Based on product analysis, low‐temperature spectroscopic observations, high‐level quantum‐mechanical computations, viscosity effect, and laser‐flash photolysis, the puckered singlet diradicaloid puc‐1 DR6 was assigned to the new 450 nm absorption. The latter was detected experimentally at the same time as the planar singlet diradical pl‐1 DR6 . Sterically demanding substituents as well as viscosity impediments were essential for the detection of the experimentally hitherto unknown puckered singlet cyclopentane‐1,3‐diyl diradicaloid puc‐1 DR6 , that is, the third isomer in homolysis. The present findings should stimulate future work on the mechanistically fascinating stereoselectivity documented in the formation of bicyclo2.1.0]pentanes during the 2,3‐diazabicyclo2.2.1]heptane denitrogenation. |
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Keywords: | mass spectrometry photochemistry radical reactions reactive intermediates UV/Vis spectroscopy |
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