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In chemistry, HOMO and LUMO are types of molecular orbitals. The acronyms stand for highest occupied molecular orbital and lowest unoccupied molecular orbital , respectively. HOMO and LUMO are sometimes collectively called the frontier orbitals , such as in the frontier molecular orbital theory .
The HOMO of butadiene and the LUMO of ethene are both antisymmetric (rotationally symmetric), meaning the reaction is allowed.* In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the endo -product is favored, a result best explained through FMO theory.
The highest occupied molecular orbital and lowest unoccupied molecular orbital are often referred to as the HOMO and LUMO, respectively. The difference of the energies of the HOMO and LUMO is called the HOMO-LUMO gap. This notion is often the matter of confusion in literature and should be considered with caution.
The filled MO highest in energy is called the highest occupied molecular orbital (HOMO) and the empty MO just above it is then the lowest unoccupied molecular orbital (LUMO). The electrons in the bonding MO's are called bonding electrons and any electrons in the antibonding orbital would be called antibonding electrons. The reduction in energy ...
The original rationale behind Lewis acid-catalyzed Diels–Alder reactions is incorrect, [39] [48] [49] [50] because besides lowering the energy of the dienophile's LUMO, the Lewis acid also lowers the energy of the HOMO of the dienophile and hence increases the inverse electron demand LUMO-HOMO orbital energy gap. Thus, indeed Lewis acid ...
The constant β in the energy term is negative; therefore, + = + with + = (+) is the lower energy corresponding to the HOMO energy and = with = is the LUMO energy. If, contrary to the Hückel treatment, a positive value for S := S 12 = S 21 {\displaystyle S:=S_{12}=S_{21}} were included, the energies would instead be
The Diels-Alder reaction of hexadeca-1,3,5,7,9,11,13,15-octaene and ethylene can be thought of as a [4+2] reaction between a substituted diene and a dienophile. The frontier molecular orbitals produced by a typical structural optimization are as follows: the HOMO and LUMO of the dienophile "ethylene" are two-centered, while the HOMO and the LUMO of the substituted diene "hexadeca-1,3,5,7,9,11 ...
This is because α-nucleophiles showing the α-effect have smaller HOMO(nucleophile)-LUMO(substrate) gap, in other words, high HOMO energy level that allows more orbital interaction. Examples of α-nucleophiles with α-effects are shown in Figure 4. The α-nucleophiles have smaller HOMO lobes than the parent normal nucleophile. Figure 4.