Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Departamento de Química, Instituto de Ciências Naturais, Universidade Federal de Lavras, 37200-900, Lavras, MG, Brazil.
Phys Chem Chem Phys. 2021 Sep 29;23(37):20883-20891. doi: 10.1039/d1cp02502c.
The concept of dipolar repulsion has been widely used to explain several phenomena in organic chemistry, including the conformational preferences of carbonyl compounds. This model, in which atoms and bonds are viewed as point charges and dipole moment vectors, respectively, is however oversimplified. To provide a causal model rooted in quantitative molecular orbital theory, we have analyzed the rotational isomerism of haloacetaldehydes OHC-CHX (X = F, Cl, Br, I), using relativistic density functional theory. We have found that the overall trend in the rotational energy profiles is set by the combined effects of Pauli repulsion (introducing a barrier around that separates minima at and ), orbital interactions (which can pull the minimum towards to maximize hyperconjugation), and electrostatic interactions. Only for X = F, not for X = Cl-I, electrostatic interactions push the preference from to . Our bonding analyses show how this trend is related to the compact nature of F the more diffuse nature of the heavier halogens.
偶极排斥的概念已被广泛用于解释有机化学中的几个现象，包括羰基化合物的构象偏好。然而，该模型将原子和键分别视为点电荷和偶极矩向量，过于简化。为了提供一个基于定量分子轨道理论的因果模型，我们使用相对论密度泛函理论分析了卤代乙醛 OHC-CHX（X = F、Cl、Br、I）的旋转异构现象。我们发现，旋转能谱的总体趋势是由 Pauli 排斥（在 处引入一个势垒，将最小值与 隔开）、轨道相互作用（可以将 最小值拉向 以最大化超共轭）和静电相互作用的综合影响决定的。只有对于 X = F，而不是 X = Cl-I，静电相互作用才会推动从 到 的偏好。我们的键分析表明，这种趋势与 F 的紧凑性质以及较重卤素的更扩散性质有关。
