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Regiochemical Substituent Switching of Spin States in Aryl(trifluoromethyl)carbenes and Ortho Substituent Effect on Aryl(trifluoromethyl)carbenes
AdvisorSheridan, Robert S.
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Part 1.Using B3LYP calculations, we show that a trifluoromethyl group can stabilize singlet versus triplet carbenes by a small, but systematic amount vs. hydrogen. Geometry and natural bond orbital analysis suggests that the strong inductive electron-withdrawing effect of a trifluoromethyl group can cause rehybridization at the carbenic centers. The trifluoromethyl group also increases the electron affinity of the carbenes, in parallel with observed increased reactivity for C-H insertion. We found ammonium cationic ligands give novel singlet ground spin state carbenes via a strongly electron-withdrawing group produced orbital rehybridization. Much of these results have been published: Song, M.-G.; Sheridan, R. S. J. Phys. Org. Chem. 2011, 24, 889. Part 2.We have investigated methoxy substituted phenyl(trifluoromethyl)carbenes by means of matrix isolation techniques and DFT studies. For para and meta cases, the regiochemical substitution switching of spin states were investigated. We synthesized carbene precursors, and generated the corresponding carbenes at cryogenic temperatures. The generated carbenes were characterized by spectroscopic methods, such as IR and UV/vis. Using various trapping reagents and EPR spectroscopy, we confirmed their different ground spin states. These results were also supported by DFT studies. Much of these results have been published: Song, M.-G.; Sheridan, R. S. J. Am. Chem. Soc. 2011, 133, 19688. For an ortho methoxy substituent, we observed an unusual UV/vis spectroscopic behavior of the diazirine. The reason for the difference was studied with DFT calculations. The corresponding carbene generation, reactions with various spin trapping reagents, EPR spectroscopy, and photochemistry were studied. Part 3. We have investigated an isolation of nitroxyl (HNO) as a single component in solid matrices at cryogenic temperature. We have attempted a clean isolation of nitroxyl using matrix isolation, studied its reactivity, and searched for other stable HNO sources