- Excited-state hydroxide ion release from a series of acridinol photobases
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The excited-state heterolysis of acridinol-based derivatives leads to the release of the OH-ion and the formation of the corresponding acridinium cations. To evaluate the parameters that control the reaction barriers, the kinetics of excited-state OH-release from a series of acridinol photobases were studied using transient absorption spectroscopy. The rate constants were obtained in three solvents (methanol, butanol, and isobutanol), and the data were modeled using Marcus theory. The intrinsic reorganization energies obtained from these fits were found to correlate well with the solvent reorganization energies calculated using dielectric continuum model, suggesting that the excited-state OH-release occurs along the solvent reaction coordinate. Furthermore, the ability of acridinol photobases to photoinitiate chemical reactions was demonstrated using the Michael reaction between dimethylmalonate and nitrostyrene.
- Xie, Yun,Ilic, Stefan,Skaro, Sanja,Maslak, Veselin,Glusac, Ksenija D.
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p. 448 - 457
(2017/12/08)
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- Pseudobase formation from 9-substituted 10-methylacridinium cations in aqueous solution
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Rates of cation-pseudobase equilibration have been measured for a series of C-9 substituted (CH3, CH3CH2, C6H5CH2, (CH3)2CH, C6H5, 4-(CH3)2NC6H4) 10-methylacridinium cations in aqueous solution at 25 deg C over the pH range of approximately 9-13.Separation of the rate constants for formation (kOH) and decomposition (k2) of each of these pseudobases allowed the calculation of the pKR(1+) value for each cation.The presence of a C-9 isopropyl substituent enhances the stability of the pseudobase relative to the cation, whereas all other C-9 substituted cations have pKR(1+) values greater than the 10-methylacridinium cation.There is no simple quantitative relationship between pKR(1+) and the size of the C-9 substituent.Rate constants (kOH) for hydroxide ion attack on these C-9 substituted cations are in the order: H>primary alkyl>secondary alkyl>aryl>, while rate constants (k2) for pseudobase decomposition are less predictable but generally follow the order: H>primary alkyl>aryl>secondary alkyl.These phenomena are shown to be consistent with a competition between destabilization of the cation by peri interactions between the C-9 substituent and H(1) and H(8) and reduced pseudobase solvation for large C-9 substituents.Resonance interactions of 9-aryl substituents with the acridine moiety of these cations are shown to be quite small. 9-Aryl-10-methylacridinium cations are approximately 30-fold more reactive towards hydroxide ion attack than are their triphenylmethyl carbocation analogues.
- Bunting, John W.,Chew, Vivian S. F.,Abhyankar, Sudhir B.,Goda, Yukiko
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p. 351 - 354
(2007/10/02)
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