Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, D-52074, Aachen, Germany.
Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010, Créteil, France.
Phys Chem Chem Phys. 2023 Mar 15;25(11):7688-7696. doi: 10.1039/d2cp05774c.
High-resolution spectroscopy techniques play a pivotal role to validate and efficiently benchmark available methods from quantum chemistry. In this work, we analyzed the microwave spectrum of ethyl butyrate within the scope of a systematic investigation to benchmark state-of-the-art exchange-correlation functionals and methods, to accurately predict the lowest energy conformers of carbonyl compounds in their isolated state. Under experimental conditions, we observed two distinct conformers, one of and one of symmetry. As reported earlier in the cases of some ethyl and methyl alkynoates, structural optimizations of the most abundant conformer that exhibits a symmetry proved extremely challenging for several quantum chemical levels. To probe the sensitivity of different methods and basis sets, we use the identified soft-degree of freedom in proximity to the carbonyl group as an order parameter. The results of our study provide useful insight for spectroscopists to select an adapted method for structure prediction of carbonyl compounds based on their available computational resources, suggesting a reasonable trade-off between accuracy and CPU cost. At the same time, our observations and the resulting sets of highly accurate experimental constants from high-resolution spectroscopy experiments give an appeal to theoretical groups to look further into this seemingly simple family of chemical compounds, which may prove useful for the further development and parametrization of theoretical methods in computational chemistry.
高分辨率光谱技术在验证和有效基准量子化学中可用方法方面发挥着关键作用。在这项工作中，我们在系统研究的范围内分析了丁酸乙酯的微波光谱，以基准最先进的交换相关泛函和方法，准确预测羰基化合物在其孤立状态下的最低能量构象。在实验条件下，我们观察到两种不同的构象，一种为 对称，另一种为 对称。正如早些时候在一些乙基和甲基炔酸酯的情况下报道的那样，对于几个量子化学水平，对表现出 对称的最丰富构象进行结构优化被证明极具挑战性。为了探究不同方法和基组的敏感性，我们将靠近羰基的识别出的软自由度用作序参数。我们的研究结果为光谱学家提供了有用的见解，以便根据可用的计算资源选择适应于羰基化合物结构预测的方法，在准确性和 CPU 成本之间提出了合理的折衷。同时，我们的观察结果和高分辨率光谱实验得出的高精度实验常数集，呼吁理论小组进一步研究这一看似简单的化合物家族，这可能对计算化学中理论方法的进一步发展和参数化有用。
