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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Oxide Radical Anion Reactivity with Aliphatic Amino Compounds in Aqueous Solution: Comparison of H-Atom Abstraction from C-H and N-H Groups by ·O~- and ·OH Radicals
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Oxide Radical Anion Reactivity with Aliphatic Amino Compounds in Aqueous Solution: Comparison of H-Atom Abstraction from C-H and N-H Groups by ·O~- and ·OH Radicals

机译：与脂肪族氨基化合物在水溶液中的氧化物自由基阴离子反应性：·O〜-和·OH自由基从C-H和N-H基团提取H-原子的比较

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One-electron oxidants react with H_2N-CHRR' amino compounds by electron transfer (ET), and direct H abstraction from N-H and C-H, giving respectively, aminium (~(·+)NH_2CHRR'), aminyl (NH-CHRR'), and -C-centered radicals (H_2N-CRR'). The yields of these species from ·O~- reactions with the anions of glycine (Gly-), alanine (Ala-), and -methylalanine (MeAla-) and with methylamine (MeNH_2) have been investigated at pH 13. The results indicate an ET process is negligible. Aminyl and α-C-centered radicals appear to be formed only by direct H abstraction reactions. In line with this, the ratios of the overall rates of H abstraction from N-H and C-H, kN(-H)/kC(-H), for ~·O~- reacting with different amino compounds decrease with C-H bond dissociation enthalpy (BDE) and thus follow the pattern expected for direct abstraction reactions. In contrast to ~·O~-, the conjugate OH radical produces significant yields of aminium radicals by ET, which evidently contribute to aminyl radical formation by subsequent proton loss from nitrogen. Thus, the kN(-H)/kC(-H) ratios for OH are higher than those for ~·O~- and do not decrease regularly with C-H BDE. Formation of α-C-centered radicals via ET and subsequent proton loss from a C-H group of the aminium radical is much less likely. The overall rates of H abstraction from C-H sites by both ~·OH and ~·O~- are found to increase with the exothermicity of the reaction. Because of its spherical symmetry the steric factors for ~·O~- reactions are larger than those for ~·OH, but in most cases this appears to be compensated by more favorable potential energy surfaces stemming from the 36 kJ mol~(-1) greater exothermicity of ~·OH reactions. ~·O~- reactions with charged species are of course also susceptible to the effects of Coulombic interactions.
机译：一电子氧化剂通过电子转移（ET）与H_2N-CHRR'氨基化合物反应，并直接从NH和CH提取H，分别得到铵（〜（·+）NH_2CHRR'），氨基（NH-CHRR'），和-C中心自由基（H_2N-CRR'）。在pH值为13的条件下，研究了·O〜-与甘氨酸（Gly-），丙氨酸（Ala-）和-甲基丙氨酸（MeAla-）的阴离子以及与甲胺（MeNH_2）的反应的产率。这些结果表明ET过程可以忽略不计。氨基和以α-C为中心的自由基似乎仅通过直接的H抽象反应形成。与此相符的是，与不同氨基化合物发生〜·O〜-反应时，从NH和CH提取H的总比率kN（-H）/ kC（-H）的比率随CH键解离焓（BDE）的降低而降低。 ），因此遵循直接抽象反应的预期模式。与〜·O〜-相反，共轭OH自由基通过ET产生大量的氨基自由基，这显然是由于随后质子从氮中损失而导致了氨基自由基的形成。因此，OH的kN（-H）/ kC（-H）比高于〜·O〜-，并且对于C-H BDE不会有规律地降低。通过ET形成以α-C为中心的自由基以及随后从铝自由基的C-H基团损失质子的可能性大大降低。发现〜·OH和〜·O〜-均从C-H位提取H的总速率随反应放热而增加。由于~~ O〜-反应的空间对称性，其~~ O〜-反应的空间因子大于~~ OH，但在大多数情况下，这似乎由36 kJ mol〜（-1）产生的更有利的势能面所补偿。 〜·OH反应放热大。与带电物质发生的〜·O〜-反应当然也容易受到库仑相互作用的影响。

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