On the electronic character of localized singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals: substituent effects on the lifetime.
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 approximately CN, H approximately Me, Me > H, H. This unprecedented substituent effect reveals stabilization of the singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals 3 through radical, zwitterionic, pi-bonding, and hyperconjugative structures.
Abe
Manabu
M
Department of Materials Chemistry, Graduate School of Engineering, Osaka University, Suita 565-0871, Osaka, Japan. abe@ap.chem.eng.osaka-u.ac.jp
Adam
Waldemar
W
Hara
Michihiro
M
Hattori
Masanori
M
Majima
Tetsuro
T
Nojima
Masatomo
M
Tachibana
Kei
K
Tojo
Sachiko
S