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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Conformational landscape of diisopropyl ketone: Quantum chemical calculations validated by microwave spectroscopy
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Conformational landscape of diisopropyl ketone: Quantum chemical calculations validated by microwave spectroscopy

机译：二异丙基酮的构象景观：微波光谱法验证的量子化学计算

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摘要

We report on the gas-phase structure of the most abundant conformer of diisopropyl ketone, (CH_3)_2HC-CO-CH(CH_3) 2_, as observed by molecular beam Fourier transform microwave spectroscopy. The gas-phase structures of five conformers of diisopropyl ketone were optimized using ab initio calculations at the MP2/6-311++G(d,p) level of theory. The natures of the stationary points were verified using harmonic frequency calculations. The only conformer observed in the supersonic jet possesses C_2 symmetry and appears as an enantiomeric pair. From the microwave spectrum, a set of three highly accurate rotational constants, five centrifugal distortion constants, and three sextic centrifugal distortion constants were determined. The structure of the observed conformer was optimized again at different levels of theory using the HF, MP2, and B3LYP methods. The theoretical constants of the C_2 conformer were subsequently validated using the experimental constants. To understand the transitions of one conformer to the others, the isopropyl groups were rotated against each other. The resulting two-dimensional potential energy surface shows nicely the symmetry of the conformational landscape and also indicates the enantiomeric pairs of the conformers. The barriers to internal rotation of the methyl groups were determined to be 1052 and 905 cm~(-1) at the MP2/6-311++G(d,p) and the B3LYP/6-311++G(d,p) levels, respectively. In agreement with the theoretical predictions, no internal rotation patterns could be observed in the microwave spectrum.
机译：我们报道了分子束傅里叶变换微波光谱法观察到的最丰富的二异丙基酮（CH_3）_2HC-CO-CH（CH_3）2_构象异构体的气相结构。在MP2 / 6-311 ++ G（d，p）的理论水平上，使用从头算来优化五个构象的二异丙基酮的气相结构。使用谐波频率计算验证了固定点的性质。在超声速射流中观察到的唯一构象异构体具有C_2对称性，并显示为对映体对。从微波光谱中，确定了一组三个高精度旋转常数，五个离心畸变常数和三个性别离心畸变常数。使用HF，MP2和B3LYP方法在不同的理论水平上再次优化了观察到的构象异构体的结构。随后使用实验常数验证C_2构象异构体的理论常数。为了理解一种构象异构体向另一种构象异构体的转变，将异丙基彼此相对旋转。所得的二维势能面很好地显示了构象景观的对称性，并且还指示了构象体的对映体对。确定在MP2 / 6-311 ++ G（d，p）和B3LYP / 6-311 ++ G（d）处，甲基内部旋转的壁垒为1052和905 cm〜（-1）， p）水平。与理论预测一致，在微波光谱中没有观察到内部旋转模式。

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