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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Combined FTIR Matrix Isolation and Ab Initio Studies of Pyruvic Acid: Proof for Existence of the Second Conformer
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Combined FTIR Matrix Isolation and Ab Initio Studies of Pyruvic Acid: Proof for Existence of the Second Conformer

机译：结合的FTIR基质分离和丙酮酸的从头算研究：第二种构象异构体存在的证据

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摘要

The molecular structure of pyruvic acid was investigated by matrix isolation FTIR spectroscopy, density functional theory (DEl’), and ab initio calculations performed at the RHF, MP2, MP4(SDQ), and CCSD(T) levels of theory with the aug-cc-pVDZ basis set. In these calculations, the geometries of the three lowest energy conformers of pyruvic aci4 were fully optimized at the DFT/B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ levels. Additionally, the relative energies of the conformers were calculated at the MP4, CCSD, and CCSD(T) levels. Harmonic frequencies and IR intensities were then calculated for these three conformers and were used to account for the zero point vibrational energy corrections and to assist the assignment of the observed bands to the different forms. We found that two conformers are present in the Ar matrix, and both forms exhibit a planar framework with the carbonyl bonds in a trans arrangement but differ in the orientation of the hydroxyl hydrogen. By varying the temperature of the pyruvic acid vapor prior to matrix deposition we were able to separate the bands due to the two conformers and measure their enthalpy difference. The spectral signature of the second pyruvic acid conformer has been identified for the first time. Experimental enthalpy difference between the two most stable conformers was found to be 8.7(±15%) kJ mol~(-1), which is in good agreement with the theoretical result.
机译：丙酮酸的分子结构通过基质分离FTIR光谱，密度泛函理论（DEl'）进行了研究，并从头开始计算了RHF，MP2，MP4（SDQ）和CCSD（T）的理论水平，结果为8月。 cc-pVDZ基础集。在这些计算中，在DFT / B3LYP / aug-cc-pVDZ和MP2 / aug-cc-pVDZ水平下，丙酮酸aci4的三个最低能量构象异构体的几何结构得到了最优化。此外，在MP4，CCSD和CCSD（T）水平上计算构象异构体的相对能量。然后计算这三个构象的谐波频率和IR强度，并用于说明零点振动能量校正并协助将观察到的频带分配给不同形式。我们发现Ar矩阵中存在两个构象异构体，并且两种形式都显示出带有羰基键的反式排列的平面构架，但是羟基氢的取向不同。通过在基质沉积之前改变丙酮酸蒸气的温度，我们能够分离出由于两个构象异构体引起的谱带，并测量它们的焓差。首次鉴定出第二丙酮酸构象剂的光谱特征。发现两个最稳定构象异构体之间的实验焓差为8.7（±15％）kJ mol〜（-1），与理论结果吻合良好。

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