Unraveling the Bürgi-Dunitz Angle with Precision: The Power of a Two-Dimensional Energy Decomposition Analysis

Understanding the geometrical preferences in chemical
reactions
is crucial for advancing the field of organic chemistry and improving
synthetic strategies. One such preference, the Bürgi-Dunitz
angle, is central to nucleophilic addition reactions involving carbonyl
groups. This study successfully employs a novel two-dimensional Distortion-Interaction/Activation-Strain
Model in combination with a two-dimensional Energy Decomposition Analysis
to investigate the origins of the Bürgi-Dunitz angle in the
addition reaction of CN– to (CH3)2CO. We constructed a 2D potential energy surface defined
by the distance between the nucleophile and carbonylic carbon atom
and by the attack angle, followed by an in-depth exploration of energy
components, including strain and interaction energy. Our analysis
reveals that the Bürgi-Dunitz angle emerges from a delicate
balance between two key factors: strain energy and interaction energy.
High strain energy, as a result of the carbonyl compound distorting
to avoid Pauli repulsion, is encountered at high angles, thus setting
the upper bound. On the other hand, interaction energy is shaped by
a dominant Pauli repulsion when the angles are lower. This work emphasizes
the value of the 2D Energy Decomposition Analysis as a refined tool,
offering both quantitative and qualitative insights into chemical
reactivity and selectivity.

探明化学反应中的几何偏好，对于推动有机化学学科发展、优化合成策略至关重要。其中，伯吉-迪尼茨角（Bürgi-Dunitz angle）是涉及羰基的亲核加成反应的核心研究对象。本研究创新性地采用二维畸变-相互作用/活化-应变模型（two-dimensional Distortion-Interaction/Activation-Strain Model）结合二维能量分解分析（two-dimensional Energy Decomposition Analysis），探究了氰根负离子（CN–）与丙酮[(CH3)2CO]加成反应中伯吉-迪尼茨角的起源。本研究构建了以亲核试剂与羰基碳原子间距、进攻角度为变量的二维势能面，随后对包括应变能与相互作用能在内的能量组分展开了深入剖析。分析结果表明，伯吉-迪尼茨角源于应变能与相互作用能两大关键因素间的精妙平衡：当进攻角度较大时，羰基化合物为规避泡利排斥发生畸变，会产生较高的应变能，从而限定了伯吉-迪尼茨角的上限；反之，当进攻角度较小时，相互作用能主要由泡利排斥主导。本研究凸显了二维能量分解分析作为精细化研究工具的应用价值，可为化学反应活性与选择性的研究提供定量与定性双重维度的解析。