氮苄叉基苯胺分子的平面扭曲驱动力的DFT研究

为了探索DFT方法中氮苄叉基苯胺分子的扭曲驱动力, 通过把非平面氮苄叉基苯胺(NBA)分子的DFT能量分成π和σ的方法, 分析了垂直离域能ΔE^V(θ)及σ-π轨道作用能ΔE^σπ(θ)的失稳定性, 并讨论了在扭曲过程中它们所起的作用. 在B3LYP/6-31G*, 6-311G*, 6-31G(2d), 6-311G(2d)水平下的计算结果显示: 与经典观点不同, π电子的离域是失稳定的, 且平面时失稳定性最强, 是分子扭曲的动力; 但σ-π轨道作用也是失稳定的, 随着扭角的增大其失稳定性增强, 是分子扭曲的阻力. NBA分子的大扭角构象, 是包含π-π, σ-π轨道作用在内的各种电子相互作用共同作用的结果.

DFT Study of Driving Force for Distorting Benzylideneaniline Molecule Away from Planar Geometry

In order to understand the nature of the driving force for distorting the non-planar molecule benzylideneaniline (NBA) away from its planar geometry, two energy effects, the vertical resonance energy DE^V(θ) and the σ-π orbital interaction energy ΔE^σπ(θ), were calculated with the DFT method, and then partitioned into their π and σ parts, denoted as DE^V-π(θ) and DE^V-σ(θ), DE^(σπ)-π(θ) and DE^(σπ)-σ(θ) respectively. DE^V(θ) is always destabilizing, and has a tendency to distort NBA molecule away from its planar geometry as far as possible. Similarly, DE^σπ(θ) is also destabilizing, however, it is most destabilizing at the θ＝90° geometry. NBA molecule would prefer the θ＝90° geometry if there were no interaction between the σ and p systems. The fact dE^T(θ)/dθ＝0 (total energy) around θ＝40° geometry, is a compromise between the various orbital interactions including π-π, σ-π interactions.