14 documents found, page 1 of 2
A protocol for the investigation of the intramolecular vibrational energy redis...
Duarte, Leonardo J.; Nunes, Cláudio M.; Fausto, Rui; Braga, Ataualpa A. C.The conformational isomerization of nitrous acid (HONO) promoted by excitation of the νOH or νN[double bond, length as m-dash]O stretching normal coordinates is the first observed case of an infrared-induced photochemical reaction. The energy captured by the excited normal modes is redistributed into a highly excited vibrational level of the τOH torsion normal coordinate, which is the isomerization reaction coo...
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 ...
Inducing molecular reactions by selective vibrational excitation of a remote an...
Nunes, Cláudio M.; Pereira, Nelson A. M.; Viegas, Luís P.; Pinho e Melo, Teresa M. V. D.; Fausto, RuiWe demonstrate here that selective vibrational excitation of a moiety, remotely attached in relation to the molecular reaction site, might offer a generalized strategy for inducing bond-breaking/ bond-forming reactions with exquisite precision. As a proof-ofprinciple, the electrocyclic ring-expansion of a benzazirine to a ketenimine was induced, in a cryogenic matrix, by near-IR light tuned at the overtone stre...
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...
Conformational isomerizations triggered by vibrational excitation of second str...
Nunes, Cláudio M.; Reva, Igor; Fausto, RuiVibrational excitation using frequency-tunable IR laser light has been developed as a powerful tool for selective manipulation of molecular conformations. In this methodology, vibrational excitation has been typically applied to the first stretching overtones (∼80 kJ mol-1) but also to the fundamental modes (∼40 kJ mol-1). Here, we demonstrate that selective conformational isomerizations are also achieved using...
Effects of Entangled IR Radiation and Tunneling on the Conformational Interconv...
Jesus, A. J. Lopes; Nunes, Cláudio M.; Reva, Igor; Pinto, Sandra M V; Fausto, RuiThe conformers of 2-cyanophenol (2CP) and their interconversions were studied by infrared (IR) spectroscopy after trapping the monomers of the gaseous compound into low-temperature (15 K) argon (Ar) and nitrogen (N2) matrixes. To assist in the interpretation of the experimental results, B3LYP, MP2, and QCISD electronic structure calculations were carried out for the 2CP molecule. Two planar conformers, cis and ...
Intermolecularly-induced conformational disorder in ferrocene, 1-bromoferrocene...
Silva, Patrícia A.; Maria, Teresa M. R.; Nunes, Cláudio M.; Eusébio, Maria Ermelinda S.; Fausto, RuiConformational preferences for isolated molecules of ferrocene, 1-bromoferrocene and 1,1′-dibromoferrocene were obtained by combined use of matrix-isolation infrared spectroscopy and quantum chemical calculations. Monomeric ferrocene and 1-dibromoferrocene were found to exist in a low temperature argon matrix (T = 15 K) exclusively in the eclipsed configuration, which corresponds to their most stable conformati...
Near-IR laser generation of a high-energy conformer of L-alanine and the mechan...
Nunes, Cláudio M.; Lapinski, Leszek; Fausto, Rui; Reva, IgorMonomers of L-alanine (ALA) were isolated in cryogenic nitrogen matrices at 14 K. Two conformers were identified for the compound trapped from the gas-phase into the solid nitrogen environment. The potential energy surface (PES) of ALA was theoretically calculated at the MP2 and QCISD levels. Twelve minima were located on this PES. Seven low-energy conformers fall within the 0-10 kJ mol(-1) range and should be ...
Cycloaddition of trifluoromethyl azafulvenium methides: synthesis of new triflu...
Nunes, Cláudio M.; Silva, Manuela Ramos; Beja, Ana Matos; Fausto, Rui; Melo, Teresa M. V. D. Pinho eThe chemistry of trifluoromethyl azafulvenium methides was explored leading to a new route to trifluoromethylpyrrole-annulated systems. The first evidence of azafulvenium methides acting as 1,3-dipoles is reported. These azafulvenium methides showed site selectivity in the reaction with strong electron-deficient dipolarophiles leading exclusively to 1,3-cycloadducts. In the cycloaddition with less-activated dip...
4-Halo-1,3-oxazoles: Unambiguous structural assignment of 2-halo-2-benzoyl-2H-a...
Lopes, Susy; Nunes, Cláudio M.; Fausto, Rui; Melo, Teresa M. V. D. Pinho ehttp://www.sciencedirect.com/science/article/B6TGS-4T9CD1T-2/2/97ced5a20f3a7c031b52a8483cc8ee76