Competition between Hydrogen Bonding and Proton Transfer during Specific Anion Recognition by Dihomooxacalix[4]arene Bidentate Ureas

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• 作者：Eduardo Martínez-González ; Felipe J. González ; José R. Ascenso ; Paula M. Marcos ; Carlos Frontana
• 刊名：Journal of Organic Chemistry
• 出版年：2016
• 出版时间：August 5, 2016
• 年：2016
• 卷：81
• 期：15
• 页码：6329-6335
• 全文大小：414K
• 年卷期：0
• ISSN：1520-6904

文摘

Competition between hydrogen bonding and proton transfer reactions was studied for systems composed of electrogenerated dianionic species from dinitrobenzene isomers and substituted dihomooxacalix[4]arene bidentate urea derivatives. To analyze this competition, a second-order E_rC_rC_i mechanism was considered where the binding process is succeeded by proton transfer and the voltammetric responses depend on two dimensionless parameters: the first related to hydrogen bonding reactions, and the second one to proton transfer processes. Experimental results indicated that, upon an increase in the concentration of phenyl-substituted dihomooxacalix[4]arene bidentate urea, voltammetric responses evolve from diffusion-controlled waves (where the binding process is at chemical equilibrium) into irreversible kinetic responses associated with proton transfer. In particular, the 1,3-dinitrobenzene isomer showed a higher proton transfer rate constant (∼25 M^–1 s^–1) compared to that of the 1,2-dinitrobenzene (∼5 M^–1 s^–1), whereas the 1,4-dinitrobenzene did not show any proton transfer effect in the experimental conditions employed.