Semi-empirical calculation of reactivity ratios

From the specific refractive index, the UV absorption maximum is calculated which measures the difference between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Subtracting the HOMO‐LUMO energy from the π–π° transition energy of ethylene renders an estimation of the total π‐energy. The difference between the sum of the total π‐energies of reactants and the energy of the transition state approximates the activation energy and relates to the reactivity ratio.