Chirality influence on the aggregation of methyl mandelate
Chirality influence on the aggregation of methyl mandelate
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DOI：
10.1039/c0nj00142b
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发表时间：
2010-01-01
影响因子：
3.3
通讯作者：
Zischang, Julia
中科院分区：
文献类型：
--
作者：
Albrecht, Merwe;Borba, Ana;Zischang, Julia
采用多种技术研究了扁桃酸甲酯的聚集模式，揭示了聚集单体的相对手性对其聚集模式的影响。基质分离证实单一单体构象占上风。二聚体的电子谱受相对单体手性的强烈影响。与MP2和DFT-D计算结果相比，振动效应更加微妙，可以用最稳定的同位和异位二聚体结构来解释。选择性红外/紫外双共振技术和宽带红外光谱技术为手性鉴别现象提供了基本一致的光谱指纹图谱。优势的同手性二聚体有两个分子间O- h中心点中心点O=C氢键，而结合更强的异手性二聚体只有一个这样的氢键。这是分散与分子内或分子间氢键竞争的结果。芳香相互作用也在三聚体和更大的簇中发挥作用，有利于同手性环排列。相似之处和差异，充分研究乳酸甲酯体系强调。体相表现出不同氢键模式之间的竞争。对映纯的、外消旋的和3:1的晶体包含了无限的具有不同排列的芳香族基团的氢键链。它们表现出明显不同的挥发性，对映纯化合物比外消旋晶体更易挥发。积累的实验和量子化学证据使扁桃酸甲酯成为色散力和氢键相互作用在手性判别中竞争作用的模型系统。
The methyl ester of mandelic acid is investigated by a wide range of techniques to unravel its aggregation pattern and the influence of relative chirality of the aggregating monomers. Matrix isolation confirms that a single monomer conformation prevails. The electronic spectrum of the dimers is strongly affected by the relative monomer chirality. Vibrational effects are more subtle and can be explained in terms of the most stable homo- and heteroconfigurational dimer structures, when compared to results of MP2 and DFT-D computations. Selective IR/UV double resonance techniques and wide-band FTIR spectroscopy provide largely consistent spectroscopic fingerprints of the chirality discrimination phenomena. The dominant homochiral dimer has two intermolecular O-H center dot center dot center dot O=C hydrogen bonds whereas the more strongly bound heterochiral dimer involves only one such hydrogen bond. This is a consequence of the competition between dispersion and intramolecular or intermolecular hydrogen bonding. Aromatic interactions also play a role in trimers and larger clusters, favoring homochiral ring arrangements. Analogies and differences to the well-investigated methyl lactate system are highlighted. Bulk phases show a competition between different hydrogen bond patterns. The enantiopure, racemic, and 3 : 1 crystals involve infinite hydrogen-bonded chains with different arrangements of the aromatic groups. They exhibit significantly different volatility, the enantiopure compound being more volatile than the racemic crystal. The accumulated experimental and quantum-chemical evidence turns methyl mandelate into a model system for the role of competition between dispersion forces and hydrogen bond interactions in chirality discrimination.