Two-dimensional Hückel molecular orbital theory

The simple Hückel molecular orbital theory is extended to include hydrocarbons with sp-hybridization in addition to the sp²-hybridization. Molecular orbitals are constructed as linear. combinations of 2p orbitals in two dimensions perpendicular to each other. Total π bond orders (P) are defined and cover the range up to P = 2 in the two-dimensional case. The relationship between bond orders and CC bond lengths is studied. The theory is applied to nine hydrocarbons, which include systems with conjugated and cumulated double bonds as well as triple bonds. Calculated bond lengths from the bond orders are found to agree within ±0.03 Å with experimental values.