Publications

Abstract A qualitative and quantitative energetic and structural study of dibenzyl ketone (DBK) and benzyl ethyl ketone (BEK) was carried out in order to obtain insights into the type and magnitude of aromatic interactions that these systems present in their different phases. The crystal structure of DBK was obtained by X-ray crystallography, and it shows that the conformation adopted in the crystalline state is governed by the intermolecular interactions. The standard (p(0) = 10(5) Pa) molar enthalpy of formation in the gaseous state at T = 298.15 K was derived by Calvet and combustion calorimetry. Using a homodesmic reaction scheme, the first calorimetric evaluation of the interaction enthalpy between two stacked phenyl rings is presented. A stabilizing enthalpic effect of (12.9 +/- 4.9) kJ mol(-1) associated with the intramolecular pi-pi interaction in DBK was found. The gas phase intramolecular pi ... pi interaction in DBK is in agreement with quantum chemical calculations at B3LYP/6-311++ G(d, p) and MP2 with various basis-sets. An intramolecular pi ... pi interaction in DBK and a weak C-H ... pi interaction in BEK were found by variable-temperature (1)H-NMR spectroscopy in MeOD. These observations are consistent with a hindered rotor interpretation, supported by ab initio calculations for the gas phase at the MP2/cc-pVDZ level. The global results indicate a distinct molecular structure on going from crystalline DBK to liquid, gas, and solution phases, ruled by the overall contribution of the intra- and intermolecular interactions.

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.