6 documents found, page 1 of 1
Dual Photochemistry of Benzimidazole
Roque, José P. L.; Rosado, Mário T. S.; Fausto, Rui; Reva, IgorMonomers of benzimidazole trapped in an argon matrix at 15 K were characterized by vibrational spectroscopy and identified as 1H-tautomers exclusively. The photochemistry of matrix-isolated 1H-benzimidazole was induced by excitations with a frequency-tunable narrowband UV light and followed spectroscopically. Hitherto unobserved photoproducts were identified as 4H- and 6H-tautomers. Simultaneously, a family of ...
Matrix Isolation in Heterocyclic Chemistry
Roque, José P. L.; Nunes, Cláudio M; Fausto, RuiHerein, we describe studies relevant to heterocyclic chemistry carried out with low-temperature matrix isolation technique in conjugation with infrared (IR) spectroscopy. These studies comprise structural characterizations, ultraviolet (UV) and thermal reactivity, IR-induced processes, and quantum tunneling reactions. Focus is given mainly to examples from recent investigations conducted in our group. Unprecede...
UV-Induced Photochemistry of 1,3-Benzoxazole, 2-Isocyanophenol, and 2-Cyanophen...
Reva, Igor; Jesus, A. J. Lopes; Nunes, Cláudio M; Roque, José P. L.; Fausto, RuiThe monomers of 1,3-benzoxazole isolated in a cryogenic argon matrix were characterized by infrared spectroscopy. The photochemistry of matrix-isolated 1,3-benzoxazole, induced by excitation with a frequency-tunable narrowband UV light, was investigated. Irradiation at 233 nm resulted in a nearly quantitative conversion of 1,3-benzoxazole into 2-isocyanophenol. The individual photochemical behavior of the in si...
Switching on H-Tunneling through Conformational Control
Roque, José P. L.; Nunes, Cláudio M.; Viegas, Luís P.; Pereira, Nelson A. M.; Pinho e Melo, Teresa M. V. D.; Schreiner, Peter R.; Fausto, RuiH-tunneling is a ubiquitous phenomenon, relevant to fields from biochemistry to materials science, but harnessing it for mastering the manipulation of chemical structures still remains nearly illusory. Here, we demonstrate how to switch on H-tunneling by conformational control using external radiation. This is outlined with a triplet 2-hydroxyphenylnitrene generated in an N2 matrix at 10 K by UV-irradiation of ...
Kinetically unstable 2–isocyanophenol isolated in cryogenic matrices: Vibration...
Jesus, A. J. Lopes; Reva, Igor; Nunes, Cláudio M.; Roque, José P. L.; Pinto, Sandra M. V.; Lourenço, Rui FaustoMonomers of 2-isocyanophenol were generated in low-temperature solid Ar and N2 matrices by UV-irradiation of benzoxazole and characterized by infrared (IR) spectroscopy. Near–IR narrowband excitation of the first OH-stretching overtone of 2–isocyanophenol isolated in an N2 matrix converted the most stable cis into the higher-energy trans conformer. Interconversions between these conformers also occurred when th...
Heavy-Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of...
Nunes, C. M.; Viegas, Luís P.; Wood, Samuel A.; Roque, José P. L.; McMahon, Robert J.; Rui FaustoNot long ago, the occurrence of quantum mechanical tunneling (QMT) chemistry involving atoms heavier than hydrogen was considered unreasonable. Contributing to the shift of this paradigm, we present here the discovery of a new and distinct heavy-atom QMT reaction. Triplet syn-2-formyl-3-fluorophenylnitrene, generated in argon matrices by UV-irradiation of an azide precursor, was found to spontaneously cyclize t...