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Reactivity of Molecular Oxygen in Ground and Excited State: Why is Singlet Oxygen Super-Reactive?

#chemistry #photochemistry #molecular #education #oxygen #anticancer #quantumphysics #quantumtheory #molecularorbitaltheory This is an edited video-lecture for chemists that are interested in molecular oxygen, photochemistry and singlet oxygen. The triplet ground state of molecular oxygen and the excited state, singlet oxygen, are discussed. (A similar lecture has been presented for BSc students, for MSc students, for PhD students as well as for Professors at an institutional talk). For more information on PDT and singlet oxygen, see also    • The Photochemistry of Photodynamic (a...   (and text below video, for references) Learning objectives: 1 Molecular oxygen has a triplet ground state, responsible for many of its special properties. It has "bi-radial character". We need the Lewis structure with the double bond as well as the Lewis structure with the two unpaired electrons (with the same spin) to describe it, in a simple way. 2 Singlet oxygen, the delta form, can react similar to ozone, it can result in similar reaction products. We can use the zwitter-ionic resonance form of singlet oxygen to describe some of its reactivity. 3 Lewis structures of excited states can be very useful, and give insight, in a different way. We have to use quantum mechanics to describe the system fully, and as good as we can. It can help to than translate the full quantum chemical results into "simplified Lewis structure of excited states". We do that on a regular basis for charge transfer states as well as for push-pull chromophores. https://doi.org/10.3906/kim-0811-33 (Figure 4) https://doi.org/10.1039/B818371F (Figure 10) https://doi.org/10.1002/cphc.200500127 (computations) https://doi.org/10.1142/9789814327824... (Figure 7) https://doi.org/10.1039/c2pp05378k (Figure 6) https://doi.org/10.1039/c9pp00399a (Figure 13, 14, 15, in an abstract way) https://doi.org/10.1002/chem.202001494 (scheme 1) https://www.researchgate.net/profile/... Some related work on molecular oxygen: The most important information presented in this video can be found on pages 583-586 of Modern Molecular Photochemisry, by Nicolas J. Turro, 1991. Hoffman https://doi.org/10.1021/jacs.7b04232 Greer (Ene reaction) https://doi.org/10.1021/ja027225p Turro & Murthy 1976: https://doi.org/10.1021/ja00437a088 (picture with zwitterionic form!!) "Thus, the reaction of 1 and singlet oxygen produces an intermediate whose decomposition results in formation of excited states of 2. This intermediate is stable for days at —90 °C. Reaction of 1 with the phosphorus ozonides 39a and 49b also results in chemiluminescence at temperatures below 0 °C." DFT https://doi.org/10.1063/1.2217733 Ogilby papers: https://doi.org/10.1039/B926014P Wilkinson papers https://doi.org/10.1063/1.555965 https://doi.org/10.1063/1.555934 YouTube lectures on singlet oxygen reactivity:    • Photoreduction and singlet oxygen pho...   (note mistake in MO scheme of oxygen!!).    • Mod-01 Lec-20 Singlet Oxygen Chemistry   (at ~9:10 zwitter-ionic form of singlet oxygen is used!!) ADDITION: 20-04-2023 see also Figure 3 in: Journal of Porphyrins and Phthalocyanines J. Porphyrins Phthalocyanines 2001; 5: 105–129 REVIEW Basic principles of photodynamic therapy IAN J. MACDONALD* and THOMAS J. DOUGHERTY https://doi.org/10.1002/jpp.328 ADDITION: 08-11-2024 For a Frontier Molecular Orbital description of singlet oxygen reactivity, see: https://doi.org/10.1002/recl.19800990908 "A frontier orbital description of the reaction of singlet oxygen with simple aromatic systems" by C. J. M. van den Heuvel, J. W. Verhoeven, Th. J. de Boer (available through Sci-Hub). oxygen v2 28 01 2023