Degree: Doctor

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FCUP

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Showing 5 latest publications. Total publications: 20
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1. Thermochemical studies on 3-methyl-quinoxaline-2-carboxamide-1,4-dioxide derivatives: Enthalpies of formation and of N-O bond dissociation, Gomes, JRB; Sousa, EA; Gomes, P; Vale, N; Goncalves, JM Pandey, S; Acree, WE; da Silva, MDMCR in JOURNAL OF PHYSICAL CHEMISTRY B, 2007, ISSN: 1520-6106,  Volume: 111, 
Article,  Indexed in: crossref, scopus, wos  DOI: 10.1021/jp06818c P-004-BJF
Abstract The standard molar enthalpies of formation of the 3-methyl-N-R-2-quinoxalinecarboxamide-1,4-dioxides (R = H, phenyl, 2-tolyl) in the gas phase were derived using the values for the enthalpies of combustion of the crystalline compounds, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, at T = 298.15 K. These values have also been used to calibrate a computational procedure that has been employed to estimate the gas-phase enthalpies of formation of the corresponding 3-methyl-N-R-2-quinoxalinecarboxamides and also to compute the first, second, and mean N-O bond dissociation enthalpies in the gas phase. It is found that the size of the substituent almost does not influence the computed N-O bond dissociation enthalpies; the maximum enthalpic difference is similar to 5 kJ center dot mol(-1).

2. Energetic and structural characterization of 2-R-3-methylquinoxaline-1,4-dioxides (R = benzoyl or tert-butoxycarbonyl): experimental and computational studies, Gomes, JRB; Sousa, EA; Goncalves, JM Gales, L; Damas, AM; Gomes, P; Pandey, S; Acree, WE; Ribeiro da Silva, MDMC in JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 2007, ISSN: 0894-3230,  Volume: 20, 
Article,  Indexed in: crossref, scopus, wos  DOI: 10.1002/poc.1184 P-004-959
Abstract The gaseous standard molar enthalpies of formation of two 2-R-3-methylquinoxaline-1,4-dioxides (R = benzoyl or tert-butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2-tert-butoxycarbonyl-3-methylquinoxaline-1,4-dioxide has been obtained by X-ray crystallography showing that the two N-O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas-phase after computations performed at the B3LYP/6-311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N-O bonds for quinoxaline 1,4-dioxide derivatives. As found previously, similar N-O bond lengths in quinoxaline-1,4-dioxide compounds are not linked with N-O bonds having the same strength. Copyright (c) 2007 John Wiley & Sons, Ltd.

3. Energetics of the N-O bonds in 2-hydroxyphenazine-di-N-oxide, Gomes, JRB; Sousa, EA; Goncalves, JM Monte, MJS Gomes, P; Pandey, S; Acree, WE; da Silva, MDMCR in JOURNAL OF PHYSICAL CHEMISTRY B, 2005, ISSN: 1520-6106,  Volume: 109, 
Article,  Indexed in: crossref, scopus, wos  DOI: 10.1021/jp051350g P-000-1WB
Abstract The standard enthalpy of formation and the enthalpy of sublimation of crystalline 2-hydroxyphenazine-diN-oxide, at T = 298.15 K, were determined from isoperibol static bomb combustion calorimetry and from Knudsen effusion experiments, as -76.7 +/- 4.2 kJ center dot mol(-1) and 197 5 kJ center dot mol(-1), respectively. The sum of these two quantities gives the standard enthalpy of formation in the gas-phase for this compound, Delta(f)H(m)degrees(g) = 120 6 KJ center dot mol(-1). This value was combined with the gas-phase standard enthalpy of formation for 2-hydroxyphenazine retrieved from a group estimative method yielding the mean (N-O) bond dissociation enthalpy, in the gas-phase, for 2-hydroxyphenazine-di-N-oxide. The result obtained with this strategy is < DHmdegrees (N - O)> = 263 +/- 4 KJ center dot mol(-1), which is in excellent agreement with the B3LYP/6-311+G(2d,2p)// B3LYP/6-31G(d) computed value, 265 KJ center dot mol(-1).

4. Thermochemistry of 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide. Evaluation of the mean dissociation enthalpy of the (N-O) bond, da Silva, MDMCR Gomes, JRB; Goncalves, JM Sousa, EA; Pandey, S; Acree, WE in ORGANIC & BIOMOLECULAR CHEMISTRY, 2004, ISSN: 1477-0520,  Volume: 2, 
Article,  Indexed in: crossref, scopus, wos  DOI: 10.1039/b408250h P-000-DB7
Abstract The standard enthalpy of formation of the 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide compound in the gas-phase was derived from the enthalpies of combustion of the crystalline solid measured by static bomb combustion calorimetry and its enthalpy of sublimation determined by Knudsen mass-loss effusion at T=298.15 K. This value is (383.8+/-5.4) kJ mol(-1) and was subsequently combined with the experimental gas-phase enthalpy of formation of atomic oxygen and with the computed gas-phase enthalpy of formation of 2-amino-3-quinoxalinecarbonitrile, (382.0+/-6.3) kJ mol(-1), in order to estimate the mean (N-O) bond dissociation enthalpy in the gas-phase of 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide. The result obtained is (248.3+/-8.3) kJ mol(-1), which is in excellent agreement with the B3LYP/6-311+G(2d,2p)//B3LYP/631G(d) computed value.

5. Molecular thermochemical study of Ni(II), Cu(II) and Zn(II) complexes with N,N '-bis(salicylaldehydo)ethylenediamine, da Silva, MDMCR Goncalves, JM Silva, ALR; Oliveira, PCFC; Schroder, B; da Silva, MAVR in JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, 2004, ISSN: 1381-1169,  Volume: 224, 
Article,  Indexed in: crossref, scopus, wos  DOI: 10.1016/j.molcata.2004.09.008 P-000-7AB
Abstract The standard (p(0) = 0.1 MPa) molar enthalpies of formation, at T= 298.15 K, of crystalline Ni(II), Cu(II) and Zn(II) complexes with N,N'-bis(salicylaldehydo)ethylenediamine (H(2)salen) were determined by solution-reaction calorimetry measurements as, respectively. Delta(f)H(m)(-) {[Ni(salen)], cr}=-(226.1 +/- 3.9)kJmol(-1), DeltafH(m)(o) {[Cu(salen)], cr}=-(139.0 +/- 3.9)kJmol(-1) and Delta(f)H(m)(o) {[Zn(salen)], cr}=-(281.3 +/- 4.6)kJmol(-1). The standard molar enthalpies of sublimation of the same metal complexes, at T=298.15K, were obtained by effusion methods as Delta(cr)(g)H(m)(o), [Ni(salen)]=(163.9+/-3.2)kJmol(-1), Delta(cr)(g)H(m)(o) [Cu(salen)]=(175.3 +/- 2.7)kJmol(-1) and Delta(g)(cr)H(m)(o) [Zn(salen)]=(179.6 +/- 3.7)kJmol(-1). The differences between the mean metal-ligand and hydrogen-ligand bond dissociation enthalpies were derived and discussed in terms of structure, in comparison with identical parameters for complexes of the same metals with other tetradentate Schiff bases involving a N2O2 donor set.