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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Conformational space and vibrational spectra of methyl 4-chloro-5-phenyl-1, 3-oxazole-2-carboxylate
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Conformational space and vibrational spectra of methyl 4-chloro-5-phenyl-1, 3-oxazole-2-carboxylate

机译：4-氯-5-苯基-1，3-恶唑-2-羧酸甲酯的构象空间和振动光谱

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摘要

Methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate (MCPOC) has been synthesized and isolated in cryogenic matrices (argon and xenon). FTIR spectroscopy studies on the matrix isolated compound, supported by DFT(B3LYP)/6-311++G(d,p) calculations, allow for the identification of two low-energy conformers (I and II) of the molecule, which differ from each other in the orientation of the ester group relative to the oxazole ring. In both these conformers, the ester moiety is in the s-cis configuration (O - C - O - CH_3 dihedral: 0°). Conformer II is ca. 3.0 kJ mol~1 higher in energy than form I in the gas phase. Two additional higher energy conformers, III and IV, with relative energies of ca. 30 and 45 kJ mol ~1, respectively, were predicted to exist by the calculations, corresponding to structures where the ester group is in an approximately s-trans arrangement. Annealing of the compound isolated in xenon at 60 K led to aggregation and simultaneous reduction of the population of I compared to that of the more polar conformer II. These results suggest the inversion of the order of stability of the two conformers in that matrix, eventually accompanied by a higher trend of conformer I to aggregate. Full assignment of the observed infrared bands to the two experimentally accessible conformers was carried out for the matrix isolated monomeric species. In addition, the infrared spectra of the neat compound in the low-temperature (10 K) amorphous and crystalline phases, as well as the infrared and Raman spectra of the crystal at room temperature were also obtained and assigned.
机译：已合成4-氯-5-苯基-1,3-恶唑-2-羧酸甲酯（MCPOC），并在低温基质（氩气和氙气）中分离。在DFT（B3LYP）/ 6-311 ++ G（d，p）计算的支持下，对基质分离的化合物进行FTIR光谱研究，可以鉴定该分子的两个低能构象体（I和II）在酯基相对于恶唑环的方向上彼此独立。在这两个构象异构体中，酯部分均呈s-顺式构型（OC-OC-CH_3二面角：0°）。符合者II为约。在气相中，能量比形式I高3.0 kJ mol〜1。另外两个较高能量的构象异构体III和IV，相对能量为ca。通过计算预测分别存在30和45 kJ mol〜1，对应于酯基呈近似s-反式排列的结构。与极性更大的构象异构体II相比，在60 K的氙气中分离的化合物退火导致I的聚集和同时减少。这些结果表明在该基质中两个构象异构体的稳定性顺序颠倒，最终伴随着构象异构体I聚集的更高趋势。对于基质分离的单体物种，将观察到的红外波段完全分配给两个实验可访问的构象异构体。另外，还获得并分配了低温（10 K）非晶态和结晶相中纯化合物的红外光谱，以及室温下晶体的红外和拉曼光谱。

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