UNIFIED TOPOLOGY OF FRONTIER MOLECULAR ORBITALS TO EXPLAIN PERICYCLIC REACTIONS

In this work is proposed a didactic alternative vision to teach pericyclic reactions. To this end, they were classified according to the connectivity of reactants systems, as connected atom reactions (CAR) and the other possibility, as not connected atom reactions (NOCAR). Electrocyclic reactions and sigmatropic rearrangements are examples of CAR categorization, and the cycloadditions being NOCAR. With these two categories, a pedagogical alternative description is proposed to the orbital topology in reactants to explain the pericyclic reactions. According to this classification, the HOMO's topology is adequate to all CAR, while the traditional HOMO-LUMO's topology is adequate to NOCAR. All issues typically deduced by the traditional treatment, such as allowed and forbidden reactions, and stereochemical aspects are also explained by the alternative approach.

本研究提出了一种用于教学周环反应的替代教学视角。为此，本研究根据反应物体系的连接方式对周环反应进行分类：分为连接原子反应（Connected Atom Reactions, CAR）与非连接原子反应（Not Connected Atom Reactions, NOCAR）两类。电环化反应与σ迁移重排属于CAR类别的典型示例，而环加成反应则属于NOCAR类别。基于这两类分类，本研究提出了一种针对反应物轨道拓扑结构的教学性替代描述方案，用于阐释周环反应的相关原理。根据该分类体系，所有CAR类反应均适用于最高占据分子轨道（Highest Occupied Molecular Orbital, HOMO）拓扑分析，而传统的最高占据分子轨道-最低未占据分子轨道（Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital, HOMO-LUMO）拓扑分析则适用于NOCAR类反应。该替代方法同样能够阐释传统方法中推导得出的所有结论，包括反应的允许/禁阻特性以及立体化学相关问题。