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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >The Free Energies of Reactions of Chlorinated Methanes with Aqueous Monovalent Anions: Application of Ab Initio Electronic Structure Theory
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The Free Energies of Reactions of Chlorinated Methanes with Aqueous Monovalent Anions: Application of Ab Initio Electronic Structure Theory

机译：氯化甲烷与一价阴离子水溶液反应的自由能：从头算电子结构理论的应用

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摘要

The presence of different anionic species in natural waters can significantly alter the degradation rates of chlorinated methanes and other organic compounds. Favorable reaction energetics is a necessary feature of these nucleophilic substitution reactions that can result in the degradation of the chlorinated methanes. In this study, ab initio electronic structure theory is used to evaluate the free energies of reaction of a series of monovalent anionic species (OH~-, SH~-, NO_(3~-), HCO_(3~-), HSO_(3~-), HSO_(4~-), H_2PO_(4~-), and F~-) that can occur in natural waters with the chlorinated methanes, CCl_4, CCl_3H, CCl_2H_2, and CClH_3. The results of this investigation show that nucleophilic substitution reactions of OH~-, SH~-, HCO_(3~-), and F~- are significantly exothermic for chlorine displacement, NO_(3~-) reactions are slightly exothermic to thermoneutral, HSO_(3~-) reactions are slightly endothermic to thermoneutral and HSO_(4~-), and H_2PO_(4~-) reactions are significantly endothermic. In the case of OH~-, SH~-, and F~- where there are limited experimental data, these results agree well with experiment. The results for HCO_(3~-) are potentially important given the near ubiquitous occurrence of carbonate species in natural waters. The calculations reveal that the degree of chlorination, with the exception of substitution of OH~-, does not have a large effect on the Gibbs free energies of the substitution reactions. These results demonstrate that ab initio electronic structure methods can be used to calculate the reaction energetics of a potentially large number of organic compounds with other aqueous species in natural waters and can be used to help identify the potentially important environmental degradation reactions.
机译：天然水中存在不同的阴离子物种会显着改变氯化甲烷和其他有机化合物的降解率。有利的反应能是这些亲核取代反应的必要特征，其可导致氯化甲烷的降解。在本研究中，从头算电子结构理论用于评估一系列单价阴离子物种（OH〜-，SH〜-，NO_（3〜-），HCO_（3〜-），HSO_（ 3〜-），HSO_（4〜-），H_2PO_（4〜-）和F〜-）可以在天然水中与氯化甲烷，CCl_4，CCl_3H，CCl_2H_2和CClH_3一起发生。研究结果表明，OH〜-，SH〜-，HCO_（3〜-）和F〜-的亲核取代反应对于氯置换有明显的放热作用，NO_（3〜-）反应对热中性有放热作用， HSO_（3〜-）反应对热中性和HSO_（4〜-）略有吸热，而H_2PO_（4〜-）反应则显着吸热。在OH〜-，SH〜-和F〜-的情况下，实验数据有限，这些结果与实验吻合得很好。鉴于天然水中几乎无处不在的碳酸盐物种，HCO_（3〜-）的结果可能具有重要意义。计算结果表明，氯化度，除OH〜-的取代外，对取代反应的吉布斯自由能没有很大的影响。这些结果证明，从头算电子结构方法可用于计算天然水中潜在大量有机化合物与其他水性物质的反应能，并可用于帮助识别潜在的重要环境降解反应。

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