Research Computing Center, University of North Carolina , Chapel Hill, North Carolina 27599-3420, United States.
J Phys Chem A. 2013 Feb 7;117(5):962-5. doi: 10.1021/jp312521z. Epub 2013 Jan 29.
Bond rotations are common and important in molecular studies such as drug design and enzymatic reactions. Steric hindrance and hyperconjugation are often borrowed to justify the origin of bond rotation barriers. However, there exists no consensus, even for as simple molecules as ethane, on which the effect is more significant. Here, we show that a unified view is possible. To that end, we employ two energy partition schemes from density functional theory to investigate the flexible rotation barrier of six molecules with one rotatable dihedral angle: ethane, methylamine, methanol, hydrazine, hydroxylamine, and hydrogen peroxide. Our results suggest that, even though steric and quantum effects play indispensable roles, it is the electrostatic interaction that governs the barrier height of all these different types of systems. This work not only consolidates earlier views about the role of steric and quantum effects, it also provides new insights about the origin and nature of the bond rotation barrier, which should be applicable to many different types of chemical bonds.
键旋转在药物设计和酶反应等分子研究中很常见且非常重要。为了说明键旋转势垒的起源，人们经常借用空间位阻和超共轭来解释。然而，即使对于乙烷等简单分子，对于哪种效应更为显著，也没有共识。在这里，我们展示了一种统一的观点。为此，我们采用两种密度泛函理论中的能量分割方案来研究六个具有一个可旋转二面角的分子的柔性旋转势垒：乙烷、甲胺、甲醇、肼、羟胺和过氧化氢。我们的结果表明，尽管空间位阻和量子效应起着不可或缺的作用，但决定所有这些不同类型体系势垒高度的是静电相互作用。这项工作不仅巩固了关于空间位阻和量子效应作用的早期观点，还为键旋转势垒的起源和本质提供了新的见解，这应该适用于许多不同类型的化学键。
