page_title: Möbius–Hückel concept
section_title: The generalized Möbius–Hückel orbital arrays
hierarchical_section_title: Möbius–Hückel concept / The generalized Möbius–Hückel orbital arrays
caption_attribution_description: English: A drawing for the Moebius-Hueckel Concept Article
context_page_description: The Möbius–Hückel treatment is one of two predicting reaction allowedness versus forbiddenness. The concept is the counterpart of the Woodward–Hoffmann approach. The methodology in this treatment utilizes the plus-minus sign parity in proceeding around a cycle of orbitals in a molecule or reaction while the Woodward–Hoffmann methodology uses a large number of rules with the same consequences.
context_section_description: The two orbital arrays in Figure 3 are just examples and do not correspond to real systems. In inspecting the Möbius one on the left, plus-minus overlaps are seen between orbital pairs 2-3, 3-4, 4-5, 5-6 and 6-1, corresponding to an odd number 5 as required by a Möbius system. Inspection of the Hückel one on the right, plus-minus overlaps are seen between orbital pairs 2-3, 3-4, 4-5, and 6-1, corresponding to an even number 4 as required by a Hückel system.
  The plus-minus orientation of each orbital is arbitrary since these are just basis set orbitals and do not correspond to any molecular orbital. If any orbital were to change signs, two plus-minus overlaps are either removed or added and the parity (evenness or oddness) is not changed. One choice of signs leads to zero plus-minus overlaps for the Hückel array on the right.
caption: Figure 3. Möbius (left) and Hückel (right) orbital arrays.