Two simple acylnitrenes, 2-furoylnitrene (2) and 3-furoylnitrene (6), were generated through 266 nm laser photolysis of the corresponding azides. Both are magnetically bistable in cryogenic matrices, as evidenced by the direct observation of the closed-shell singlet state with IR spectroscopy in solid Ne, Ar, Kr, Xe, and N matrices (3-40 K) and the triplet state in toluene (10 K) with EPR spectroscopy (2: |D/hc| = 1.48 cm and |E/hc| = 0.029 cm; 6: |D/hc| = 1.39 cm and |E/hc|c = 0.039 cm). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (3 and 7) and ring-opening product 3-cyanoacrolein (9-E and 9-Z), respectively, in which the elusive 3-furylnitrene (8) was also identified by IR and EPR spectroscopy (|D/hc| = 1.12 cm and |E/hc| = 0.005 cm).
Bond homolysis (BHo) is a fundamental concept in chemical-bonding phenomena. To date, research studies on the BHo concept have provided crucial information for understanding the nature of chemical bonding and reactions. Two potential-energy minima, a σ-bonding isomer and a singlet-diradical isomer, have been known to exist in carbon-carbon BHo. Herein, a third isomer, that is, a puckered singlet diradical exhibiting unstructured long-wavelength fluorescence beyond 460 nm, was first observed in the excited states of 1,4-diarylbicyclo[2.1.0]pentane derivatives. The careful selection of appropriate substituents in the bicyclic structures enabled direct spectral detection. State-of-the-art ab initio quantum chemical calculations quantitatively reproduced the experimental observations. This new finding provides new insight into carbon-carbon bond-breaking and -forming processes.
Bond homolysis (BHo) is a fundamental concept in chemical‐bonding phenomena. To date, research studies on the BHo concept have provided crucial information for understanding the nature of chemical bonding and reactions. Two potential‐energy minima, a σ‐bonding isomer and a singlet‐diradical isomer, have been known to exist in carbon–carbon BHo. In the present study, a third isomer, that is, a puckered singlet diradical exhibiting unstructured long‐wavelength fluorescence beyond 460 nm, was first observed in the excited states of 1,4‐diarylbicyclo[2.1.0]pentane derivatives. This finding provides new insight into carbon–carbon bond‐breaking and ‐forming processes. For more information, see the Communication by M. Abe, H.‐H. G. Tsai et al. on page 7595.
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