Publications

Abstract The energetic effects caused by replacing one of the methylene groups in the 9,10-dihydroanthracene by ether or ketone functional groups yielding xanthene and anthrone species, respectively, were determined from direct comparison of the standard (p degrees = 0 1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K. of these compounds. The experimental static-bomb combustion calorimetry and Calvet microcalorimetry and the computational G3(MP2)//B3LYP method were used to get the standard molar gas-phase enthalpies of formation of xanthene. (41 8 +/- 3 5) kJ mol(-1), and anthrone, (31 4 +/- 3 2) kJ mol(-1) The enthalpic increments for the substitution of methylene by ether and ketone in the parent polycyclic compound (9,10-dihydroanthracene) are -(1179 +/- 5 5) kJ mol(-1) and -(1283 +/- 5.4) kJ mol(-1), respectively

Abstract In the title compound, C(21)H(18)N(4)O(4), there is an intramolecular N-H center dot center dot center dot O hydrogen bond between the amino H atom and an O atom of the 2-nitro group of the adjacent benzene ring. The central benzene ring forms dihedral angles of 79.98 (7) and 82.88 (7)degrees with the two phenyl rings. In the crystal structure, molecules are linked into a three-dimensional network by weak C-H center dot center dot center dot N, C-H center dot center dot center dot O and C-H center dot center dot center dot pi interactions.

Abstract The standard molar enthalpies of formation, at T = 298.15 K, of all possible single methylated derivatives of benzothiophene and dibenzothiophene were calculated by means of the G3(MP2)//B3LYP approach employing several different working reactions (homodesmotic and atomization). The most stable compounds are the 7-methylbenzothiophene and 4-methyldibenzothiophene while the least stable are the 5-methylbenzothiophene and 1-methyldibenzothiophene compounds. Calculated enthalpic increments for the reactions of methylation are in the range -29.5 and - 39.1 kJ mol(-1).

Abstract The title compound, C17H11N, crystallizes with two molecules in the asymmetric unit which are linked by a weak C-H center dot center dot center dot N hydrogen bond. The dihedral angles between the benzene ring and the naphthalene ring system in the two molecules are 60.28 (3) and 60.79 (3)degrees. In the crystal, molecules are linked into a three-dimensional network by weak C-H center dot center dot center dot pi interactions.

Abstract Thermochemical and thermophysical studies have been carried out for crystalline 3,4,4'-trichlorocarbanilide. The standard (p degrees = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for the crystalline 3,4,4'-trichlorocarbanilide (TCC) was experimentally determined using rotating-bomb combustion calorimetry, as -(234.6 +/- 8.3) kJ . mol(-1). The standard enthalpy of sublimation, at the reference temperature of 298.15 K, was measured by the vacuum drop microcalorimetric technique, using a High Temperature Calvet Microcalorimeter as (182.1 +/- 1.7) kJ . mol(-1). These two thermochemical parameters yielded the standard molar enthalpy of formation of the studied compound, in the gaseous phase, at T = 298.15 K, as -(52.5 +/- 8.5) kJ . mol(-1). This parameter was also calculated by computational thermochemistry at M05-2X/6-311++G and B3LYP/6-311++G(3df, 2p) levels, with a deviation less than 4.5 kJ . mol(-1) from experimental value. Moreover, the thermophysical study was made by differential scanning calorimetry. DSC, over the temperature interval between T = 263K and its onset fusion temperature, T = (527.5 +/- 0.4) K. A solid-solid phase transition was found at T = (428 +/- 1) K, with the enthalpy of transition of (6.1 +/- 0.1) kJ . mol(-1). The X-ray crystal structure of TCC was determined and the three-centred N-H center dot center dot center dot O=C hydrogen bonds present analyzed.

Abstract We have carried out a study of the energetics, structural, and physical properties of o-, m-, and p-hydroxybenzophenone neutral molecules, C(13)H(10)O(2), and their corresponding anions. In particular, the standard enthalpies of formation in the gas phase at 298.15 K for all of these species were determined. A reliable experimental estimation of the enthalpy associated with intramolecular hydrogen bonding in chelated species was experimentally obtained. The gas-phase acidities (GA) of benzophenones, substituted phenols, and several aliphatic alcohols are compared with the corresponding aqueous acidities (pK(a)), covering a range of 278 kJ.mol(-1) in GA and 11.4 in pK(a). A computational study of the various species shed light on structural effects and further confirmed the self-consistency of the experimental results.

Abstract The standard (p(o) = 0.1 MPa) energies of combustion in oxygen, at T = 298.15 K, for the solid compounds 2-methylpyridine-N-oxide (2-MePyNO), 3-methylpyridine-N-oxide (3-MePyNO) and 3,5-dimethylpyridine-N-oxide (3,5-DMePyNO) were measured by static-bomb calorimetry, from which the respective standard molar enthalpies of formation in the condensed phase were derived. The standard molar enthalpies of sublimation, at the same temperature, were measured by Calvet microcalorimetry. From the standard molar enthalpy of formation in gaseous phase, the molar dissociation enthalpies of the N-O bonds were derived, and compared with values of the dissociation enthalpies of other N-O bonds available for other pyridine-N-oxide derivatives.

Abstract Guiding students while they explore educational software is important in order to convey the pedagogical pragmatism that many programs seem to lack. This article points out some characteristics that we believe educational software exploration guides must contain for students to benefit from using these programs. The supporting information includes an example of an exploration guide for a chemistry educational software program about chemical equilibrium. We also briefly describe a pilot study of Portuguese high school students; the study'1s conclusions show the advantages of using exploration guides. © 2010 The American Chemical Society and Division of Chemical Education, Inc.

Abstract Dextran modified with deoxycholic acid (Dex-DCA) was synthesized by grafting DCA along the polymer backbone, with degrees of substitution (DS)-2% and 3%. The thermodynamics of the association processes of the mixed systems is followed by isothermal titration calorimetry for sodium deoxycholate/sodium dodecyl sulfate (NaDCA/NaDS), Dex-DCA with different surfactants-Dex-DCA/NaDS, Dex-DCA/NaDCA, and Dex-DCA/DTAB (dodecyltrimethylammonium bromide). Calorimetric measurements for the micellization processes of the pure surfactants in aqueous solution were also performed for comparison with the results obtained for the mixed systems. We have obtained and herein present the enthalpies of micelle formation and critical micelle concentrations for the referred pure surfactants, as well as the interaction and aggregation enthalpies for the mixed systems-surfactant/polymer. The dependence of the observed aggregation behavior on the surfactant and temperature is discussed in detail. Finally, we should stress that calorimetry allowed us to ascertain a very important fact in polymer/surfactant interaction. From the comparison between NaDCA/NaDS and Dex-DCA/NaDS calorimetric titration curves, we could clearly see that the interaction between Dex-DCA and NaDS is driven by the interaction between the bile acid moiety and the surfactant.