School of Basic Medical Sciences, Xinxiang Medical University, Xinxiang, Henan 453003, China.
Phys Chem Chem Phys. 2018 Dec 5;20(47):29601-29609. doi: 10.1039/c8cp05979a.
New gas phase infrared spectroscopy is reported for an aromatic alpha hydroxy carboxylic acid homo dimer of 9-hydroxy-9-fluorene carboxylic acid (9HFCA)2, and the hetero dimer of 9HFCA with glycolic acid. In terms of the 9-hydroxy stretching frequency, the 16 cm-1 blue-shift in the homo dimer and the 17 cm-1 blue-shift in the hetero dimer, relative to that in 9HFCA monomer, are attributed to collective effects with anti-cooperativity stronger than cooperativity. Furthermore, for the hetero dimer, the two alpha hydroxy groups' stretching frequencies are clearly resolved, and differ by 30 cm-1. This difference represents a modest, quantitative enhancement of the intramolecular H-bond by the fluorene moiety in 9HFCA monomer, as opposed to that in glycolic acid. Accurate vibrational frequencies of the alpha OH, 3568 cm-1 in the bare glycolic acid, and 3584 cm-1 in the glycolic acid homo dimer are determined for the first time by comparison to 9HFCA monomer, homo and hetero dimers. The quantitative studies by infrared spectroscopy reveal subtle interactions among intra- and intermolecular H-bonds in the alpha hydroxyl acid dimers, which are also uniquely extended to probe each monomer's subtle intramolecular interactions.
报告了一种芳香族 α-羟基羧酸同二聚体 9-羟基-9-芴甲酸（9HFCA）2 和 9HFCA 与乙醇酸的杂二聚体的新气相红外光谱。根据 9-羟基伸缩频率，同二聚体的 16cm-1 蓝移和杂二聚体的 17cm-1 蓝移相对于单体中的 9HFCA，归因于反协同作用比协同作用更强的集体效应。此外，对于杂二聚体，两个 α-羟基基团的伸缩频率明显分开，相差 30cm-1。这种差异代表了芴基部分在 9HFCA 单体中对分子内氢键的适度定量增强，而不是在乙醇酸中。通过与 9HFCA 单体、同二聚体和杂二聚体进行比较，首次确定了裸露乙醇酸中 αOH 的精确振动频率为 3568cm-1，乙醇酸同二聚体中为 3584cm-1。红外光谱的定量研究揭示了 α-羟基酸二聚体中分子内和分子间氢键之间的微妙相互作用，这些相互作用也被独特地扩展到探测每个单体的微妙分子内相互作用。
