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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Methyl formate and its mono and difluoro derivatives: Conformational manifolds, basicity, and interaction with HF theoretical investigation
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Methyl formate and its mono and difluoro derivatives: Conformational manifolds, basicity, and interaction with HF theoretical investigation

机译：甲酸甲酯及其单氟和二氟衍生物：构象流形，碱性和与HF的相互作用理论研究

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摘要

The conformational manifolds, scenarios of protonation, and hydrogen bond propensity of methyl formate and its mono and difluoro derivatives, which possess two oxygen atoms with different basicities, are studied at the B3LYP/6-311++G(3df,3pd) computational level. The optimized geometries of the title molecules, their energetics, and relevant harmonic vibrational frequencies, mainly of the ν(CH) mode of the H-C=O group, are of a primary focus. The Natural Bond Orbital analysis is invoked to obtain the second-order intra-or intermolecular hyperconjugation energies, occupations of antibonding orbitals, and hybridization of the carbon atoms. It is demonstrated that the Z conformers (and their rotamers) of the three title molecules are characterized by a higher stability compared to the E ones. The stabilities depend on the intramolecular hyperconjugative interaction and on the attraction or repulsion nonbonded interaction. The proton affinity of the carbonyl oxygen exceeds, by 15-20 kcal?mol~(-1), that of the methoxy oxygen. Fluorine substitution causes a moderate lowering of the proton affinity of the oxygens. Protonation on the oxygen atoms yields a contraction of the C-H bond and large concomitant blue shift of the ν(CH) vibration. These changes are mainly determined by a lowering of the occupation of the corresponding σ*(CH) orbitals. The esters under consideration are probed on the interaction with the HF molecule. The complexes that are formed under this interaction on the oxygen of the H-C=O group are stronger than those formed on the oxygen belonging to the methoxy one. It is deduced that the hydrogen bond energies show a linear dependence on the proton affinities of the corresponding oxygen atoms. Hydrogen-bonded complexes of moderate strength are also formed, while HF interacts with the fluorine atoms of the fluorinated esters.
机译：在B3LYP / 6-311 ++ G（3df，3pd）计算级别上研究了甲酸甲酯及其一氟和二氟衍生物的构象流形，质子化场景以及氢键倾向，该碱具有两个不同碱性的氧原子。标题分子的优化几何形状，它们的能量和相关的谐波振动频率（主要是H-C = O组的ν（CH）模）是主要重点。调用自然键轨道分析以获得二阶分子内或分子间超共轭能，反键轨道的占据以及碳原子的杂化。结果表明，三个标题分子的Z构象异构体（及其旋转异构体）与E异构体相比具有更高的稳定性。稳定性取决于分子内超共轭相互作用以及吸引或排斥非键相互作用。羰基氧的质子亲和力比甲氧基氧的质子亲和力超出15-20 kcal？mol-（-1）。氟取代导致氧的质子亲和力适度降低。氧原子上的质子化产生C-H键的收缩和ν（CH）振动的大伴随蓝移。这些变化主要是通过降低相应的σ*（CH）轨道的占有率来确定的。考察了所考虑的酯与HF分子的相互作用。在这种相互作用下在H-C ＝ O基团的氧上形成的配合物比在属于甲氧基的氧上形成的配合物更强。可以推断，氢键能与相应氧原子的质子亲和力呈线性关系。还形成了中等强度的氢键结合的配合物，而HF与氟化酯的氟原子相互作用。

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