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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Fragmentation of Radical Anions of Polyfluorinated Benzoates
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Fragmentation of Radical Anions of Polyfluorinated Benzoates

机译：多氟苯甲酸酯的自由基阴离子的裂解

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摘要

A comprehensive study of the symmetry forbidden fragmentation of short-lived radical anions (RAs) has been undertaken for the complete set of polyfluorinated benzoates (C_6F_nH_(5-n)CO_(2~-), n = 1 - 5). The decay rate constants (k_c) of RAs have been determined in aqueous alkaline solution (pH 13.4) by electron photoinjection (EPI) from mercury electrodes and were found to increase dramatically from ≤ 3 * 10~3 s~(-1) (3-F-C_6H_4CO_2~-) to (1.2 ± 0.8) * 10~9 s~(-1) (C_6F_5CO_2~-). The regioselectivity of C-F bond cleavage in the RA fragmentation has been revealed by structure assignment of reduction products of the polyfluorinated benzoic acids by Na, K, and Zn in liquid NH_3, as well as by Zn in aqueous NH_3 and aqueous alkaline solutions. The k_c values depend on the position of the cleaved fluorine to the CO_2~- group generally in the order para > ortho > meta, and to sharply increase if adjacent fluorine atoms are present. The observed trends reveal that the kinetics of the RA fragmentation reaction is not controlled by the reaction thermodynamics. Semiempirical UHF/INDO calculations, the validity of which has been confirmed by ab initio ROHF/6-31 + G calculations, were done to rationalize the observed trends. The reaction transition state (GS) was considered to arise from the RA's ∏ and Σ~* states crossing avoided due to out-of-plane deviation of the cleaving C-F bond. The satisfactory linear correlation (R = 0.96) between the model reaction energy barrier E_a and log k_c has been achieved with modeling the local solvation of the CO_2~- group by its protonation.
机译：对于完整的多氟苯甲酸酯（C_6F_nH_（5-n）CO_（2〜-），n = 1-5），已经对短寿命自由基阴离子（RAs）的对称性禁止断裂进行了全面研究。已通过汞电极的电子光注入（EPI）在碱性水溶液（pH 13.4）中确定了RA的衰减速率常数（k_c），发现其在≤3 * 10〜3 s〜（-1）时急剧增加（3 -F-C_6H_4CO_2〜-）至（1.2±0.8）* 10〜9 s〜（-1）（C_6F_5CO_2〜-）。 RA断裂中C-F键断裂的区域选择性已经通过液态NH_3中的Na，K和Zn以及NH_3水溶液和碱性水溶液中的Zn的多氟苯甲酸还原产物的结构分配来揭示。 k_c值通常取决于对位裂解的氟在CO_2-上的位置，顺序为对>邻>邻位，并且如果存在相邻的氟原子则急剧增加。观察到的趋势表明，RA片段化反应的动力学不受反应热力学的控制。进行了半经验的UHF / INDO计算，其有效性已从头算ROHF / 6-31 + G计算得到证实，以合理化所观察到的趋势。反应转变态（GS）被认为是由于裂解的C-F键的面外偏差而避免了RA的∏和Σ〜*态交叉产生的。通过对CO_2〜-基团的质子化进行局部建模，已经获得了模型反应能垒E_a和log k_c之间令人满意的线性关系（R = 0.96）。

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