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On the Electronic Character of Localized Singlet 2,2-Dimethoxycyclopentane-1,3-diyl Diradicals:  Substituent Effects on the Lifetime

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journal contribution
posted on 15.05.2002, 00:00 by Manabu Abe, Waldemar Adam, Michihiro Hara, Masanori Hattori, Tetsuro Majima, Masatomo Nojima, Kei Tachibana, Sachiko Tojo
Photodenitrogenation of the diazenes 4 affords exclusively the housanes 5 through intramolecular cyclization of the spectrally detected and characterized singlet diradicals 3. The lifetime of singlet diradical 3, determined by transient absorption measurements, depends on the Y and Z substituents at the para position of the phenyl ring and has the following order:  Y, Z = OMe, OMe ≫ OMe, CN > CN, CN > OMe, H > Cl, Cl ∼ CN, H ∼ Me, Me > H, H. This unprecedented substituent effect reveals stabilization of the singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals 3 through radical, zwitterionic, π-bonding, and hyperconjugative structures.