以密度泛函數理論對對苯酚及其衍生物的氧化反應之質子、氫原子及電子轉移反應機制之理論研究

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Title:	以密度泛函數理論對對苯酚及其衍生物的氧化反應之質子、氫原子及電子轉移反應機制之理論研究
Other Titles:	Theoretical Study on the Mechanisms of Proton, Hydrogen, Electron Transfer of p-Hydroquinone and Derivatives
Authors:	吳俊賢 Wu, Jyuhn-Hsiarn
Contributors:	佘亮 Leung, Sheh 東海大學化學系
Keywords:	電子轉移;氫原子轉移;對苯酚
Date:	2011
Issue Date:	2011-10-12T07:38:09Z (UTC)
Abstract:	本研究利用B3LYP/6-31G(d)理論計算方法探討對苯酚類衍生物與氫氧根離子、超氧陰離子進行質子轉移反應，與氧氣、超氧陰離子、 ·OOH及氫氧自由基進行氫原子與電子轉移反應的機制。總共有十二個對苯酚類衍生物，可分為帶 -SCH2COO-取代基的對苯酚類衍生物與不帶 -SCH2COO-取代基的對苯酚類衍生物，這二種有明顯差異性。帶 -SCH2COO-取代基的對苯酚類衍生物和氫氧根離子多數都能進行質子轉移反應，帶 -SCH2COO-取代基的對苯酚類衍生物和超氧陰離子則很難進行質子轉移反應，帶 -SCH2COO-取代基的對苯酚類衍生物和氧氣進行電子轉移反應比氫原子轉移反應來得容易，帶 -SCH2COO-取代基的對苯酚類衍生物和超氧陰離子進行氫原子轉移反應比電子轉移反應來得容易，帶 -SCH2COO-取代基的對苯酚類衍生物和 ·OOH及氫氧自由基都能進行氫原子及電子轉移反應。活化能方面，2,6-雙甲氧基氫?-3-硫醋酸在水溶液中與氧氣進行氫原子轉移反應的活化能比在氣態中高出約7 ~ 18 kcal/mol，2,6-雙甲氧基氫?-3-硫醋酸與氧氣及 ·OOH進行氫原子轉移反應的活化能差異不大，2,5-雙甲氧基氫?-3-硫醋酸與氧氣進行氫原子轉移反應的活化能比2,6-雙甲氧基氫?-3-硫醋酸的活化能高。 The reaction mechanisms of proton transfer of p-hydroquinone and derivatives with OH-, ?O2-, hydrogen and electron transfer of p-hydroquinone and derivatives with O2, ?O2-, ?OOH and ?OH are studied by B3LYP/6-31G(d) calculations. We have considered twelve different p-hydroquinone derivatives in total, which can be divided into two categories: with and without -SCH2COO- substituent. These two categories are quite different. The proton transfer reactions of most -SCH2COO- substituted p-hydroquinone derivatives with hydroxyl anion OH- is thermodynamically favorable; whereas those with ?O2- is not. The electron transfer reactions of p-hydroquinone derivatives with -SCH2COO- substituent and O2 are easier than their corresponding hydrogen transfer reaction; nevertheless, their hydrogen transfer reactions with ?O2- are easier than corresponding electron transfer reactions. p-hydroquinone derivatives with -SCH2COO- substituent can also make hydrogen and electron transfer reactions with ?OOH and hydroxyl radical ?OH.In aqueous solution, the activation energies of the hydrogen transfer reactions of 2,6-dimethoxyhydroquinone-3-mercaptoacetic acid with O2 calculated by PCM model in Gaussian09 are 7 ~ 18 kcal/mol higher than those in gas phase. Their hydrogen transfer reactions with O2 and ?OOH have similar activation energy barriers in gas phase. The activation energies of hydrogen transfer reactions of 2,5-dimethoxyhydroquinone-3-mercaptoacetic acid with the oxygen molecule, are in general higher than those of 2,6-dimethoxyhydroquinone-3-mercaptoacetic acid.
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