Graduate School of BASE (Bio-Applications and Systems Engineering), Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
J Phys Chem A. 2011 Sep 8;115(35):9911-8. doi: 10.1021/jp2048585. Epub 2011 Aug 11.
Infrared spectra of 2-chloro-6-fluorophenol in argon matrixes at 20 K revealed the presence of a "Cl-type" isomer, which has the OH···Cl hydrogen bond, but no "F-type" isomer with OH···F bonding, in striking contrast to the existence of both isomers in the gas and liquid phases at room temperature. This finding suggests that the F-type isomer changes to the more stable Cl-type one by hydrogen-atom tunneling in the matrixes. Similar experiments on the OD···X analog species were performed to confirm the tunneling isomerization, resulting in an O-D stretching band of the F-type isomer appearing as well as that of the Cl type, like the spectra reported in the gas and liquid phases. This implies that tunneling migration of the D atom is inhibited in the argon matrix. In addition, UV-induced photoreactions of 2-chloro-6-fluorophenol were studied by a joint use of matrix-isolation IR spectroscopy assisted by density functional theory calculations. It was found that 2-fluorocyclopentadienylidenemethanone and 4-chloro-2-fluorocyclohexadienone were produced from the Cl type; the former was by the Wolff rearrangement after dissociation of the H atom in the OH group and the Cl atom, and the latter was by intramolecular migration of the H and Cl atoms. As for the deuterated F-type isomer, however, 2-chlorocyclopentadienylidenemethanone was produced by the Wolff rearrangement after dissociation of the D atom in the OD group and the F atom, besides other photoproducts of the deuterated Cl-type isomer. It is thus concluded that the tunneling isomerization around the C-O bond occurs in the OH···X species but not in the OD···X species.
在 20 K 的氩基质中，2-氯-6-氟苯酚的红外光谱显示存在一种“Cl 型”异构体，它具有 OH···Cl 氢键，但没有 OH···F 键的“F 型”异构体，这与室温下气相和液相中两种异构体的存在形成鲜明对比。这一发现表明，在基质中通过氢原子隧穿，F 型异构体转化为更稳定的 Cl 型异构体。对 OD···X 类似物进行了类似的实验，以确认隧穿异构化，导致 F 型异构体的 O-D 伸缩带也出现了，就像在气相和液相中报告的那样。这意味着 D 原子的隧穿迁移在氩基质中受到抑制。此外，通过使用密度泛函理论计算辅助的基质隔离红外光谱学，研究了 2-氯-6-氟苯酚的光致反应。发现 Cl 型产生了 2-氟环戊二烯亚甲基酮和 4-氯-2-氟环己二烯酮；前者是在 OH 基团中的 H 原子和 Cl 原子解离后通过 Wolff 重排产生的，后者是通过 H 和 Cl 原子的分子内迁移产生的。然而，对于氘代 F 型异构体，除了氘代 Cl 型异构体的其他光产物外，OD 基团中的 D 原子和 F 原子解离后，通过 Wolff 重排产生了 2-氯环戊二烯亚甲基酮。因此，结论是 C-O 键周围的隧穿异构化发生在 OH···X 物种中，但不在 OD···X 物种中。
