Effects of Spiroconjugation on the Calculated Singlet-Triplet Energy Gap in 2,2-Dialkoxycyclopentane-1,3-diyls and on the Experimental Electronic Absorption Spectra of Singlet 1,3-Diphenyl Derivatives
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- 作者：Manabu Abe ; Waldemar Adam ; Weston Thatcher Borden ; Masanori Hattori ; David A. Hrovat ; Masatomo Nojima ; Koichi Nozaki ; and Jakob Wirz
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：January 21, 2004
- 年：2004
- 卷：126
- 期：2
- 页码：574 - 582
- 全文大小：374K
- 年卷期：v.126,no.2(January 21, 2004)
- ISSN：1520-5126
文摘
The effect of a 2,2-ethylene-ketal functionality on the singlet-triplet energy gap (
EST) and onthe first electronic transition in singlet cyclopentane-1,3-diyls (1) has been investigated. UDFT calculationspredict a significant increase in the preference for a singlet ground state in the diradical with the cyclicketal at C2 (1g; EST = -6.6 kcal/mol in C2 symmetry and -7.6 kcal/mol in C2v symmetry), compared tothe 2,2-dihydroxy- and 2,2-dimethoxy-disubstituted diradicals (1d, EST = -3.6 kcal/mol in C2 symmetry,and 1e, EST = -3.4 kcal/mol in C2 symmetry). Spiroconjugation is shown to be responsible for the largercalculated value of 
EST in 1g, relative to 1d and 1e. A strong correlation between the calculated valuesof EST and the computed electronic excitation energies of the singlet diradicals is found for diradicals 1d,1e, and 1g and for 2,2-difluorocyclopentane-1,3-diyl (1c). A similar correlation between EST and 
calcd ispredicted for the corresponding 1,3-diphenylcyclopentane-1,3-diyls 3, and the predicted blue shift in thespectrum of 3g, relative to 3e, has been confirmed by experimental comparisons of the electronic absorptionspectra of the annelated derivatives 2c, 2e, and 2g in a glass at 77 K. The wavelength of the first absorptionband in the singlet diradicals decreases in the order 2e (onset = 650 nm) > 2g (onset = 590 nm) > 2c(onset = 580 nm). The combination of these computational and experimental results provides a soundbasis for reassignment of the first electronic absorption band in singlet diradicals 2c, 2e, and 2g to theexcitation of an electron from the HOMO to the LUMO of these 2,2-disubstituted derivatives of cyclopentane-1,3-diyl.
EST) and onthe first electronic transition in singlet cyclopentane-1,3-diyls (1) has been investigated. UDFT calculationspredict a significant increase in the preference for a singlet ground state in the diradical with the cyclicketal at C2 (1g; EST = -6.6 kcal/mol in C2 symmetry and -7.6 kcal/mol in C2v symmetry), compared tothe 2,2-dihydroxy- and 2,2-dimethoxy-disubstituted diradicals (1d, EST = -3.6 kcal/mol in C2 symmetry,and 1e, EST = -3.4 kcal/mol in C2 symmetry). Spiroconjugation is shown to be responsible for the largercalculated value of EST in 1g, relative to 1d and 1e. A strong correlation between the calculated valuesof EST and the computed electronic excitation energies of the singlet diradicals is found for diradicals 1d,1e, and 1g and for 2,2-difluorocyclopentane-1,3-diyl (1c). A similar correlation between EST and calcd ispredicted for the corresponding 1,3-diphenylcyclopentane-1,3-diyls 3, and the predicted blue shift in thespectrum of 3g, relative to 3e, has been confirmed by experimental comparisons of the electronic absorptionspectra of the annelated derivatives 2c, 2e, and 2g in a glass at 77 K. The wavelength of the first absorptionband in the singlet diradicals decreases in the order 2e (onset = 650 nm) > 2g (onset = 590 nm) > 2c(onset = 580 nm). The combination of these computational and experimental results provides a soundbasis for reassignment of the first electronic absorption band in singlet diradicals 2c, 2e, and 2g to theexcitation of an electron from the HOMO to the LUMO of these 2,2-disubstituted derivatives of cyclopentane-1,3-diyl.