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Conformational Cooling Dynamics in Matrix-Isolated 1,3-Butanediol
Rosado, Mário T. S.; Jesus, António J. Lopes; Reva, Igor D.; Fausto, Rui; Redinha, José S.The complete conformational space of monomeric 1,3-butanediol has been characterized theoretically, and 73 unique stable conformers were found at the MP2/6-311++G(d,p) level. These were classified into nine families whose members share the same heavy atom backbone configurations and differ in the hydrogen atom orientations. The first and third most populated backbone families are governed by the formation of an...
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...
The structure of betaxolol from single crystal X-ray diffraction and natural bo...
Canotilho, João; Castro, Ricardo A. E.; Rosado, Mário T. S.; Silva, M. Ramos; Beja, A. Matos; Paixão, J. A.; Redinha, J. SimõesThe structure of betaxolol obtained from ethanol:water solution was studied by X-ray diffraction. The geometrical parameters needed to define the structure are tabulated. The X-ray data show the existence of two conformers in the unit cell differing only in the conformation of the cyclopropylmethoxy fragment. Differences in the bond lengths angles and dihedral between both conformations are observed. The cyclop...
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...
Enthalpy of sublimation/vaporization of trans-cyclohexyl-1,4-diamine and cis-cy...
Tomé, Luciana I. N.; Rosado, Mário T. S.; Nunes, Sandra C. C.; Maria, Teresa M. R.; Canotilho, João; Eusébio, M. Ermelinda S.The molar enthalpy of sublimation, , of trans-cyclohexyl-1,4-diamine and the molar enthalpy of vaporization, , of cis-cyclohexyl-1,2-diamine, at the temperature 298.15 K, were determined by calorimetry. was obtained for the trans-isomer and for the cis form. The molar enthalpy of fusion of the first compound, at T = 342.1 K, was determined by differential scanning calorimetry. The molar enthalpy of vaporization...
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...
Molecular Structure of Butanediol Isomers in Gas and Liquid States: Combinatio...
Jesus, A. J. Lopes; Rosado, Mário T. S.; Leitão, M. Luísa P.; Redinha, José S.Density functional theory (Becke3LYP/6-311++G**) conformational analysis was carried out for all positional butanediol isomers. Taking into account the relative populations of the most stable conformers at 298.15 K, the weighted mean enthalpies of each butanediol isomer in the gas state were computed. Combining these results with the experimental values for the enthalpies of vaporization at 298.15 K, an estimat...
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