![]() A persistent luminescence emitter emitting light for 0.1 seconds or longer after photo-irradiation of the persistent luminescence emitter stops, wherein: the persistent luminescence emitter comprises at least 70 mol % of an electron donor molecule and less than 30 mol % of an electron acceptor molecule, based on the total amount by mole of the electron donor molecule and the electron acceptor molecule, and emission intensity increases by temperature rise after photo-irradiation of the persistent luminescence emitter stops.Ģ. This is an example of the clear and simple expatiations we have prepared for over 175 reactions commonly seen in Orgo1 and Orgo2 courses.1. We hope this description has helped clarify this concepts of MO theory. We review this concept in detail in a previous article. When we do this, the HOMO of excited ethylene and LUMO of ground-state ethylene align and the reaction produces cyclobutane. However, we have the ability to excite electrons from the HOMO to a higher orbital using light (hv) or heat, thus changing the HOMO. However, in another example where we have a (2+2 cycloaddition), we see the HOMO and LUMO of ethylene do not align thus forbidding the reaction. This leads to a forward reaction and formation of the product, cyclohexene. We see that nodes of the HOMO and LUMO align that is the open and closed halves of the dumbbells align. Why? We need the electrons from a HOMO to flow from one molecule to another, so we have to use the LUMO orbital that is not occupied for this process. Then we look at the least conjugated molecule, ethylene and examine its LUMO. We start with the most conjugated molecule, butadiene and examine its HOMO. Let’s take the reaction of butadiene with ethylene, the most simplistic Diels Alder reaction (4+2 cycloaddition). Therefore, we need to use the molecular orbitals of the pi electrons to drive the reaction. Remember that cycloaddition reactions describe the formation of new C-C sigma bonds through rearrangement of the pi electrons in a conjugated system. We can extend this to ethylene and see that with 2 pi electrons, molecular orbital #1 is the HOMO and molecular orbital #2 is the LUMO. As a result, the lowest unoccupied molecular obital, or LUMO, in butadiene is #3. Therefore, the highest occupied molecular orbital, or HOMO, in butadiene is #2. It has 4 pi electrons, so we fill the lowest molecular orbitals first, two in each orbital. To determine what orbitals are occupied on your molecule, simply count how many pi bonds you have in your conjugated system. Essentially, orbitals with lower numbers of nodes (switches in the orientation of the dumbbell orbital which we show with the dashed line) behave more like bonding orbitals while orbitals with higher numbers of nodes behave like anti-bonding orbitals. Remember, there are bonding and antibonding orbitals. We describe the orientation of each half of the dumbbell orbital centered around an atom as being bold or open. The basic concept of MO theory is to describe the alternating patterns of orbitals that exist in pi bond systems. We at StudyOrgo have devised a simple explanation of the basics to MO theory to help you with your study preparations. The basics to this principle can be hard to grasp, but will be very informative in predicting the correct reaction conditions and outcome of the reaction if you understand them, which will give you a major advantage on future quizzes and exams. One of the most challenging concepts in conjugated system reactions is molecular orbital interactions, or MO theory. ![]()
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