Intramolecular and intermolecular reactivity of localized singlet diradicals: The exceedingly long-lived 2,2-diethoxy-1,3-diphenylcyclopentane- 1,3-diyl

Journal of the American Chemical Society

Volumn 122, Issue 9, 2000, Pages 2019-2026

  Abe, Manabu ^a   Adam, Waldemar ^b   Heidenfelder, Thomas ^b   Nau, Werner M ^c   Zhang, Xiangyang ^c  

^a OSAKA UNIVERSITY   (Japan)

^b UNIVERSITY OF WÜRZBURG   (Germany)

^c UNIVERSITY OF BASEL   (Switzerland)

Author keywords

[No Author keywords available]

Indexed keywords

ACETONITRILE; BENZENE; CHLOROFORM; HEXANE; RADICAL;

ABSORPTION SPECTROSCOPY; ARTICLE; CHEMICAL REACTION; ELECTRON SPIN RESONANCE; PHOTOLYSIS; SPIN TRAPPING;

EID: 0034620683     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja992507j     Document Type: Article

References (44)

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36. 2-induced mixing of the parity-forbidden transition of benzyl radicals at 460 nm with allowed transitions at higher energies has been held responsible for the strong, bathochromically shifted absorption band in the singlet diradical 2a (ref 2). An alternative interpretation, already under discussion in the previous work, would involve a transition between the symmetric and antisymmetric SOMO orbitals, which is allowed for singlet diradicals. With respect to the latter possibility, the bathochromic shift for the diethoxy-substituted diradical 2b versus the difluoro-substituted diradical 2a (by ca. 15 nm) could be due to a smaller singlet-triplet energy splitting (cf. calculated values for diradicals 15a,b in Results).
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43. The supposition that the "lower concentration" of C-H bonds in chloroform may be responsible (C-H and O-H bonds could serve to promote this chemical reaction by electronic-to-vibrational energy transfer, akin to the deactivation of singlet molecular oxygen, cf.: Gorman, A. A.; Rodgers, M. A. J. In Handbook of Organic Photochemistry; Scaiano, J. C., Ed.; CRC Press: Boca Raton, FL, 1989; Vol. II, pp 229-247), is discarded in view of the absence of a deuterium isotope effect and the "normal" behavior (short lifetime) in carbon tetrachloride (Table 2).
44. Oxygen trapping of related triplet diradicals has been previously observed in the thermally induced ring opening of the parent 1,3-diphenylbicyclo[2.1.0]pentane (Adam, W.; Platsch, H.; Wirz, J. J. Am. Chem. Soc. 1989, 111, 6896); however, unlike for the latter housane, NMR coalescence experiments could not be employed to evaluate the bond dissociation of the housane 4 to its diradical 2b due to its unsymmetric structure, i.e., anti and syn diastereomers.