Intramolecular hydrogen atom tunneling in 2-chlorobenzoic acid studied by low-temperature matrix-isolation infrared spectroscopy
Intramolecular hydrogen atom tunneling in 2-chlorobenzoic acid studied by low-temperature matrix-isolation infrared spectroscopy
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DOI：
10.1021/jp0717600
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发表时间：
2007-08-02
影响因子：
2.9
通讯作者：
Nakata, Munetaka
中科院分区：
文献类型：
--
作者：
Nishino, Satoshi;Nakata, Munetaka
采用低温基质隔离红外光谱技术，结合密度泛函理论计算，研究了2-氯苯甲酸分子内氢原子隧穿过程。在氩气和氙气基体中观察到两种相对稳定的顺式异构体SC和ST的红外光谱。当基体样品在沉积后退火时，从ST到SC的异构化发生在苯-羧基键周围。两个不太稳定的反异构体，AT，它有一个OH中心点Cl分子内氢键，和AC，它没有OH中心点Cl键，从SC和ST在UV照射后产生。当基质样品在紫外光照射后保持在黑暗中时，AT和AC通过羧基中C-O轴周围的自发异构化分别变为ST和SC。根据在不同基质温度下的吸光度变化，估算了异构化速率常数AT -> ST。的速率常数表明，在氘代的羧基基团的氢原子急剧减少。反应速率常数与基质温度的关系不符合Arrhenius定律。这些发现导致的结论是，在低温稀有气体基质中的AT -> ST和AC -> SC的异构化通过分子内氢原子隧穿进行。
Intramolecular hydrogen atom tunneling in 2-chlorobenzoic acid has been investigated by low-temperature matrix-isolation infrared spectroscopy with the aid of density functional theory calculation. Infrared spectra of two relatively stable syn isomers, SC and ST, were observed in argon and xenon matrixes. When the matrix samples were annealed after deposition, the isomerization from ST to SC occurred around the benzene-carboxyl bond. Two less stable anti isomers, AT, which has an OH center dot center dot center dot Cl intramolecular hydrogen bond, and AC, which has no OH center dot center dot center dot Cl bond, were produced from SC and ST upon UV irradiation. When the matrix samples were kept in the dark after UV irradiation, AT and AC changed to ST and SC, respectively, by spontaneous isomerization around the C-O axis in the carboxyl group. The rate constants of isomerization, AT --> ST, in a Xe matrix were estimated from the absorbance changes at various matrix temperatures. The rate constants showed a drastic decrease in deuteration of the hydrogen atom of the carboxyl group. The relationship between the rate constants and the matrix temperature did not follow the Arrhenius law. These findings lead to the conclusion that the isomerization of AT --> ST and AC --> SC in low-temperature rare-gas matrixes proceeds through intramolecular hydrogen atom tunneling.