Person: ILDIZ, GÜLCE ÖĞRÜÇ
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ILDIZ
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GÜLCE ÖĞRÜÇ
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Publication Metadata only Matrix Isolation Infrared Spectra and Photochemistry of Hydantoin(Amer Inst Physics, 2 Huntington Quadrangle, Ste 1No1, Melville, Ny 11747-4501 USA, 2013-01-31) Nunes, Claudio M.; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326Hydantoin (C3H4N2O2, 2,4-imidazolidinedione) was isolated in argon matrix at 10 K and its infrared spectrum and unimolecular photochemistry were investigated. The molecular structure of the compound was studied both at the DFT(B3LYP) and MP2 levels of approximation with valence triple- and quadruple-zeta basis sets (6-311++G(d,p); cc-pVQZ). It was concluded that the minima in the potential energy surfaces of the molecule correspond to C-1 symmetry structures. However, the energy barrier separating the two-equivalent-by-symmetry minima stays below their zero-point energy, which makes the C-s symmetry structure, which separates the two minima, the experimentally relevant one. The electronic structure of the molecule was studied in detail by performing the Natural Bond Orbital analysis of its electronic configuration within the DFT(B3LYP)/cc-pVQZ space. The infrared spectrum of the matrix isolated compound was fully assigned also with help of the theoretically predicted spectrum. Upon irradiation at lambda = 230 nm, matrix-isolated hydantoin was found to photofragment into isocyanic acid, CO, and methylenimine.Publication Metadata only Structural transformations of 3-fluoro and 3-fluoro-4-methoxy benzaldehydes under cryogenic conditions: A computational and low temperature infrared spectroscopy investigation(Elsevier Science Bv, Po Box 211, 1000 AE Amsterdam, Netherlands, 2018-05-31) Konarska, Jadwiga; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326Structural transformations of 3-fluorobenzaldehyde (C7H5FO, 3FBA) and 3-fluoro-4-methoxybenzaldehyde (C8H7FO2, 3F4MBA), taking place in different solid phase environments and at low temperature, were investigated by infrared spectroscopy, complemented by quantum chemistry calculations undertaken at the DFT(B3LYP)/6-311++G(d,p) level of approximation. The studied compounds were isolated from gas phase into cryogenic inert matrices (Ar, Xe), allowing to characterize their equilibrium conformational composition in gas-phase at room temperature. In both cases, two conformers differing by the orientation of the aldehyde moiety (with the carbonyl aldehyde bond as or trans in relation to the aromatic ring fluorine substituent) were found to coexist, with the as conformer being slightly more populated than the trans form. In situ narrowband UV irradiation of the as-deposited matrices led either to preferential isomerization of the as conformer into the trans form or decarbonylation of both conformers, depending on the used excitation wavelength. Deposition of the vapours of 3F4MBA only, onto the cold (15 K) substrate, produced an amorphous solid containing also both the as and trans conformers of the compound. Subsequent heating of the amorphous phase up to 268 K led to crystallization of the compound, which is accompanied by conformational selection, the as form being the single species present in the crystal. The experimentally observed transformations of the studied compounds, together with the structural and vibrational results obtained from the performed quantum chemical calculations, allowed a detailed structural and vibrational characterization of the individual conformers. (C) 2018 Elsevier B.V. All rights reserved.Publication Metadata only 5-Methylhydantoin: from isolated molecules in a low-temperature argon matrix to solid state polymorphs characterization(Amer Chemical Soc, 1155 16th St, Nw, Washington, Dc 20036 USA, 2017-07-20) Nogueira, Bernardo A.; Canotilho, J.; Eusebio, M. E. S.; Henriques, M. S. C.; Paixao, J. A.; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326The molecular structure, vibrational spectra and photochemistry of 5-methylhydantoin (C4H6N2O2; 5-MH) were studied by matrix isolation infrared spectroscopy and theoretical calculations at the DFT(B3LYP)/6-311++G(d,p) theory level. The natural bond orbital (NBO) analysis approach was used to study in detail the electronic structure of the minimum energy structure of 5-MH, namely the specific characteristics of the sigma and pi electronic systems of the molecule and the stabilizing orbital interactions. UV irradiation of 5-MH isolated in argon matrix resulted in its photofragmentation through a single photochemical pathway, yielding isocyanic acid, ethanimine, and carbon monoxide, thus following a pattern already observed before for the parent hydantoin and 1-methylhydantoin molecules. The investigation of the thermal properties of 5-MH was undertaken by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM) and Raman spectroscopy. Four different polymorphs of 5-MH were identified. The crystal structure of one of the polymorphs, for which it was possible to grow up suitable crystals, was determined by X-ray diffraction (XRD). Two of the additional polymorphs were characterized by powder XRD, which confirmed the molecules pack in different crystallographic arrangements.Publication Metadata only Molecular Structure, Infrared Spectra, Photochemistry, and Thermal Properties of 1-Methylhydantoin(Amer Chemical Soc, 1155 16Th St, Nw, Washington, Dc 20036 Usa, 2014-08-07) Nogueira, Bernardo A.; Canotilho, Joao; Eusebio, M. Ermelinda S.; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326The structural, vibrational, and photochemical study of 1-methylhydantoin (1-MM, C4H6N2O2) was undertaken by matrix isolation infrared spectroscopy (in argon matrix; 10 K), complemented by quantum chemical calculations performed at the DFT(B3LYP)/6-311++G(d,p) level of approximation. The theoretical calculations yielded the C-s symmetry structure, with planar heavy atom skeleton, as the minimum energy structure on the potential energy surface of the molecule. The electronic structure of this minimum energy structure of 1-MH was then studied in detail by means of the natural bond orbital (NBO) and atoms in molecules (AIM) approaches, allowing for the elucidation of specific characteristics of the molecule's sigma and pi electronic systems. The infrared spectrum of the matrix-isolated 1-MH was fully assigned, also with the help of the theoretically predicted spectrum of the compound, and its UV-induced unimolecular photochemistry (lambda >= 230 nm) was investigated. The compound was found to fragment to CO, isocyanic acid, methylenimine, and N-methyl-methylenimine. Finally, a thermal behavior investigation on 1-MM samples was carried out using infrared spectroscopy (10 K until melting), differential scanning calorimetry and polarized light thermal microscopy. A new polymorph of 1-MH was identified. The IR spectra of the different observed phases were recorded and interpreted.