| Summary: | 碩士 === 東海大學 === 化學系 === 99 === 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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