SOMOĪ SOMO is a singly occupied molecular orbital such as half-filled HOMO of a radical. Arrows show the distortion that results in a stabilizing interaction. HOMO is the highest occupied molecular orbital whereas LUMO is the lowest Unoccupied molecular orbital. (B) Superposition of the HOMO and LUMO from (A). (A) Interaction of a singly occupied p orbital (HOMO) with the a (LUMO) of planar MR3 that results in stabilization of the HOMO on pyramidalization. For example, this can help predict whether a substance will have luminescence. HOMO - LUMO interaction diagram for MR3 radicals. The band gap can sometimes serve as a measure of the excitability of the molecule: the smaller the energy, the more easily a molecule's electrons will be excited. The difference in the HOMO's energy level and the LUMO's energy level is called the band gap. The 15th MO on the list would be called the "highest occupied molecular orbital" (HOMO) and the 16th MO on the list would be the "lowest unoccupied molecular orbital" (LUMO). Compared to the HOMO orbital, in the LUMO orbital, the contribution from the single-coordinated O atom decreases, whereas the contribution of N atom increases. For example, if a molecule has enough electrons to fill 15 MOs, the 15 MOs with the lowest energy levels will be occupied. If the HOMOLUMO energy gap is small, the interaction is strong and the reac-tion is rapid, whereas if the HOMOLUMO energy gap is large, the interaction is weak and. Chemists assume that the electrons will occupy the lowest energy level MOs first. The strength of the donoracceptor interaction and the rate of cycloaddition is inversely related to the difference in energy between the HOMO and LUMO which are interacting. Chemists sort the molecular orbitals (MOs) by energy levels. HOMO and LUMO are sometimes referred to as frontier orbitals.Įach molecular orbital has a calculated energy level. The energy difference between the HOMO and LUMO is termed the HOMO-LUMO gap. LUMO stands for lowest unoccupied molecular orbital. HOMO stands for highest occupied molecular orbital. This video offers a logical overview of HOMO and LUMO molecular orbitals, especially as it applies to conjugated systems in organic chemistry reactions and mechanisms.
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