Conformational sampling and large amplitude motion of methyl valerate,Physical Chemistry Chemical Physics

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Conformational sampling and large amplitude motion of methyl valerate
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2021-1-7 , DOI: 10.1039/d0cp06057g
Ha Vinh Lam Nguyen _{1,

2,

3,

4,

5} , Maike Andresen _{1,

2,

3,

4,

5} , Wolfgang Stahl _{6,

7,

8,

9}

Affiliation

The microwave spectrum of the fruit ester methyl valerate was recorded using two molecular jet Fourier transform spectrometers covering the frequency range from 2 to 40 GHz. Quantum chemical calculations yielded 11 minima for the anti ester configuration, among them two were identified in the experimental spectrum. The methyl group in the methoxy moiety undergoes internal rotation, leading to torsional splittings of all rotational transitions into doublets. The barrier to internal rotation of the methoxy methyl group was deduced to be 417.724(70) cm⁻¹ and 418.059(27) cm⁻¹ for the C₁ and the C_s conformer, respectively, essentially the same values as those in methyl alkanoates with shorter alkyl chains, which are methyl acetate, methyl propionate and methyl butyrate. Geometry parameters such as the rotational and centrifugal distortion constants could be determined with very high accuracy. Optimisations at different levels of theory were performed for a comparison with the experimental results. The MP2/6-311++G(d,p) level of theory failed to calculate reliable rotational constants to guide the assigment of the C₁ conformer, while the MP2/cc-pVDZ level fully succeeded.

中文翻译：

戊酸甲酯的构象采样和大幅度运动

使用两个覆盖2至40 GHz频率范围的分子射流傅里叶变换光谱仪记录了水果酸酯戊酸甲酯的微波光谱。量子化学计算得出抗酯构型的最小值为11 ，其中在实验光谱中鉴定出两个。甲氧基部分中的甲基经历内部旋转，导致所有旋转转变的扭转分裂成双峰。对于C ₁和C _s，对甲氧基甲基的内部旋转的壁垒被推定为417.724（70）cm ^-1和418.059（27）cm ^-1构象分别与具有较短烷基链的链烷酸甲酯（乙酸甲酯，丙酸甲酯和丁酸甲酯）的值基本相同。诸如旋转和离心变形常数之类的几何参数可以非常高精度地确定。进行了不同理论水平的优化，以与实验结果进行比较。MP2 / 6-311 ++ G（d，p）水平的理论未能计算出可靠的旋转常数来指导C ₁构象异构体的装配，而MP2 / cc-pVDZ水平则完全成功。

更新日期：2021-01-22

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