一种改进的休克尔分子轨道模型预测纯碳环分子稳定结构

A Modified Hückel Molecular Orbital Model to Predict the Structure of Cyclo[2n]carbons

针对休克尔分子轨道(HMO)理论中只考虑相邻原子轨道相互作用的缺点,提出了一种改进的HMO模型,明确考虑间位碳原子共振积分,采用对称性匹配的分子轨道,得到了π共轭体系的能级公式,发现分子对称性降低可产生额外稳定化能,从而正确解释了纯碳环C2n分子稳定结构中键角交替变化规律,为理解二级Jahn-Teller效应提供了新思路。

Hückel Molecular Orbital(HMO) theory is popular in chemistry, but it assumes that the reduced resonance integrals exist only between the nearest-neighbor carbon atoms. Such an approximation has been justified by the explicit inclusion of the resonance integrals between the meta-directing π-bonded atoms. The energy eigenvalues are obtained using the symmetry-adapted molecular orbitals, together with the extra stabilization energy due to symmetry breaking. The polyynic geometries of cyclo[2 n]carbons with alternating angles are explained rationally using the modified HMO model, which gains new insights on the second-order Jahn-Teller effect for carbon rings.