To accurately characterize the large amplitude motions and soft degrees of freedom of isolated molecules, sampling their conformational landscape by molecular mechanics and quantum chemical calculations may provide a valuable insight into the structure and dynamics. However, the resulting models need to be validated by a reliable experimental counterpart. For ethyl pentanoates, which belong to the family of fruit esters, benchmark calculations at different levels of theory showed that the C−C bond in proximity to the ester carbonyl group exhibits a large amplitude motion that is extremely sensitive to the choice of quantum chemical method and basis set. In such cases, insights from high‐resolution molecular jet techniques are ideal to accurately identify and characterize soft degrees of freedom. Here, we report on the most abundant conformer of ethyl 2‐ethyl butyrate using Fourier‐transform microwave spectroscopy. We show that – unlike other structurally related pentanoates for which gas‐phase and crystallographic data is available – ethyl 2‐ethyl butyrate possesses a C_s symmetry plane under molecular jet conditions.

中文翻译：

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水果风味中的大幅度运动：丁酸烷基酯。

为了准确地描述孤立分子的大振幅运动和软自由度，通过分子力学和量子化学计算对它们的构象图样进行采样可以提供对结构和动力学的宝贵见解。但是，生成的模型需要由可靠的实验对象进行验证。对于属于水果酯家族的戊酸乙酯，在不同理论水平上的基准计算表明，靠近酯羰基的CC键表现出大幅度的运动，这对量子化学方法的选择极为敏感。和基础集。在这种情况下，高分辨率分子喷射技术的见解是准确识别和表征软自由度的理想选择。这里，我们使用傅里叶变换微波光谱法报告了2-乙基丁酸乙酯中最丰富的构象异构体。我们显示出-与可获得气相和晶体学数据的其他与结构相关的戊酸酯不同，2-乙基丁酸乙酯具有分子射流条件下的C _s对称平面。