We see a real-life example of this sort of " magic " in the photo above, where a student is shown pulling a strand of solid nylon from a flask that contains two immiscible solutions. It is, until we understand the details of the reaction, like a magician who puts apples and oranges in a hat, shakes it, and then pulls out rabbits and parakeets. A chemist puts one or two reagents into a flask, waits for a time, and then takes from the flask one or more completely different compounds. To the uninitiated, a chemical reaction must seem like an act of magic. In organometallic chemistry, the size of the LUMO lobe can help predict where addition to pi ligands will occur. The same analogy exists between the LUMO level and the conduction band minimum. Roughly, the HOMO level is to organic semiconductors what the valence band maximum is to inorganic semiconductors and quantum dots. The difference in energy between these two frontier orbitals can be used to predict the strength and stability of transition metal complexes, as well as the colors they produce in solution. After these assignments are made, the chemist is able to identify the Highest Occupied Molecular Orbital (HOMO) that contains electrons and the Lowest Unoccupied Molecular Orbital (LUMO) that does not contain electrons. Through qualitative molecular orbital analysis through a molecular orbital diagram, the chemist is able to display the resulting molecular orbitals stemming from atomic interaction based on their relative energies and assign bonding, nonbonding and/or antibonding character to each molecular orbital. Using molecular orbital theory, a molecular orbital diagram can be constructed that features the individual atomic basis orbitals and the molecular orbitals resulting from atomic interactions to form molecules. HOMO and LUMO are sometimes referred to as frontier orbitals. The energy difference between the HOMO and LUMO is termed the HOMO– LUMO gap. HOMO stands for highest occupied molecular orbital and LUMO for lowest unoccupied molecular orbital, respectively. HOMO and LUMO are acronyms used in orbital interaction theory of organic chemistry.
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