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Structure of the 2-isopropylaminoethanol isolated molecule: Conformational anal...
Nunes, Sandra C. C.; Eusébio, M. Ermelinda S.; Jesus, A. J. Lopes; Rosado, Mário T. S.; Redinha, J. S.In this paper, a systematic exploration of all the possible conformers of 2-isopropylaminoethanol (2-IPAE) was carried out using the Density Functional Theory (B3LYP) and the 6-311++G(d,p) basis set. At this level, 66 unique conformers within a Gibbs energy range of ca. 31 kJ mol-1 were found in the potential energy surface and their geometrical and thermodynamic properties were determined and discussed. A sign...
Structure of Isolated 1,4-Butanediol: Combination of MP2 Calculations, NBO Anal...
Jesus, A. J. Lopes; Rosado, Mário T. S.; Reva, Igor; Fausto, Rui; Eusébio, M. Ermelinda S.; Redinha, J. S.Theoretical calculations at the MP2 level, NBO and AIM analysis, and matrix-isolation infrared spectroscopy have been used to investigate the structure of the isolated molecule of 1,4-butanediol (1,4-BDO). Sixty-five structures were found to be minima on the potential energy surface, and the three most stable forms are characterized by a folded backbone conformation leading to the formation of an intramolecular...
Molecular structure of mono- and 1,2-aminoderivatives of cyclohexane: Steric st...
Tomé, Luciana I. N.; Rosado, Mário T. S.; Eusébio, M. Ermelinda S.; Redinha, J. S.The conformational study of cyclohexylamine and 1,2-cyclohexylamine derivatives was performed. The potential energy surface of every compound was calculated at B3LYP/6-31G(d) and the conformational energy minima were further optimized at B3LYP/aug-cc-pVDZ level of theory. The geometrical parameters and the electronic energy of each conformer were determined. The internal energy, enthalpy, entropy, Gibbs energy ...
Conformational Study of Monomeric 2,3-Butanediols by Matrix-Isolation Infrared ...
Jesus, A. J. Lopes; Rosado, Mário T. S.; Reva, Igor; Fausto, Rui; Eusébio, M. Ermelinda; Redinha, J. S.The FT-IR spectra of two diastereomers of 2,3-butanediol, (R,S) and (S,S), isolated in low-temperature argon and xenon matrixes were studied, allowing the identification of two different conformers for each compound. These conformers were characterized by a ±gauche arrangement around the O−C−C−O dihedral angle, thus enabling the establishment of a very weak intramolecular hydrogen bond of the O···H−O type. No o...
Stepwise conformational cooling towards a single isomeric state in the four int...
Reva, Igor D.; Jesus, António J. Lopes; Rosado, Mário T. S.; Fausto, Rui; Eusébio, M. Ermelinda; Redinha, J. S.The present work explores the possibilities of the matrix isolation technique in the structural characterisation of highly flexible molecules. To date, most studies of this type were carried out on molecules with three or less internal degrees of freedom and a few (less than 10) possible conformations. The molecule of 1,2-butanediol has four conformationally relevant three-fold rotational axes, which can result...
Enthalpy of Sublimation in the Study of the Solid State of Organic Compounds. A...
Jesus, A. J. Lopes; Tomé, Luciana I. N.; Eusébio, M. Ermelinda; Redinha, J. S.The enthalpies of sublimation of erythritol and l-threitol have been determined at 298.15 K by calorimetry. The values obtained for the two diastereomers differ from one another by 17 kJ mol-1. An interpretation of these results is based on the decomposition of this thermodynamic property in a term coming from the intermolecular interactions of the molecules in the crystal (ΔintH°) and another one related with ...
Polymorphism of pindolol, 1-(1H-indol-4-yloxyl)-3-isopropylamino-propan-2-ol
Nunes, Sandra C. C.; Eusébio, M. Ermelinda; Leitão, M. Luísa P.; Redinha, J. S.Crystallization of pindolol from the melt was studied by differential scanning calorimetry (DSC) and polarized light thermomicroscopy (PLTM) in order to discriminate the polymorphic forms obtained by this method. The crystallization process originates one exothermic signal localized in two different well-defined temperature ranges. Fusion gives rise to overlapped curves, which were analysed by peak-fitting. The...
Phase transitions of 1,2-cyclohexanediol isomers studied by polarised light mic...
Leitão, Maria Luísa Planas; Castro, Ricardo A. E.; Costa, Felisbela S.; Redinha, J. S.Polarised light microscopy and DTA have been used to study the phase transitions observed in cis and trans-1,2-cyclohexanediol during heating/cooling cycles performed between ambient and melting temperatures to prove that the presence of impurities even in trace amounts can affect the thermal properties of the substances. Good quality commercial material before and after further purification were used in this s...
Maximum likelihood estimation with nonlinear regression in polarographic and po...
Pereira, J. L. G. C.; Pais, A. A. C. C.; Redinha, J. S.In this work we review some aspects of maximum likelihood nonlinear modeling in polarographic and potentiometric techniques. Different algorithms, namely the Levenberg-Marquardt and the "error-in-variables" methods in parametric and Monte-Carlo nonparametric estimation are used. Conclusions are drawn upon the influence of experimental errors and error correlation, introduced via statistical weighting, in the ac...
Solvation of alkane and alcohol molecules. Energy contributions
Pais, A. A. C. C.; Sousa, A.; Eusébio, M. E.; Redinha, J. S.In this work we conduct a systematic ab initio study of the solvation of small alkane, monoalcohol and diol molecules, in polar solvents with different properties. A choice of basis set suitable for the type of compounds under study is presented. The various components of the solvent–solute interaction and the cavitation energy are treated individually and their variation with chain length and introduction of h...
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