Synthesis and Photochemistry of Pyridyl-Based (Trifluoromethyl) Carbenes in Low Temperature Matrices
AdvisorSheridan, Robert S.
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In this study, we examined the photochemical generation of 2- pyridyl(trifluoromethyl)carbene and 3-pyridyl(trifloromethyl)carbene in low-temperature matrices. The carbenes were generated from their previously unknown diazirine precursors, which were synthesized from bromopyridines. The diazirines were each directly deposited on the cesium iodide window of the matrix, and cooled to 10-15K. Once the diazirines were cooled, they were each irradiated with 366nm light. Both of these photolyses were monitored using IR and UVNis spectroscopy. Once we obtained these spectra, we were able to determine the electronic states of the individual carbenes. In order to predict the spin states of the new carbenes, we performed B3LYP/6- 31G** level frequency and time dependent calculations. From these calculations, we were not only able to determine the lowest energy state of the carbenes, but also their theoretical IR and UVNis spectra. We then compared the IR and UVNis spectra obtained from the matrix experiments to the theoretical spectra. From these comparisons, we found that both 2-pyridyl(trifluoromethyl)carbene and 3-pyridyl(trifluoromethyl)carbene are triplet carbenes. The calculations also showed that these triplet states are the lowest energy states of the carbenes. We found that the 2-pyridyl(trifluoromethyl)carbene prefers a conformation such that the trifluoromethyl group is pointed away from the nitrogen; however, the 3-pyridyl(trifluromethyl)carbene showed no such preference.