resumo
The relative stabilities of 2,2'- and 3,3'-bithiophenes were evaluated by experimental thermochemistry and the results compared with data obtained from state of the art calculations, which were also extended to 2,3'-bithiophene. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of crystalline 2,2'-bithiophene and 3,3'-bithiophene were calculated from the standard molar energies of combustion, in oxygen, to yield CO2 (g) and H2SO4 center dot 115H(2)O, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The vapor pressures of these two compounds were measured its a function of temperature by Knudsen effusion mass-loss technique. The standard molar enthalpies of sublimation, at T = 298.15 K, were derived from the Clausius-Clapeyron equation. The experimental values were used to calculate the standard (p degrees = 0.1 MPa) enthalpies of formation of the title compounds in the gaseous phase; the results were analyzed and interpreted in terms of enthalpic increments and molecular structure. Standard ab initio molecular orbital calculations at the G3(MP2)//B3LYP level were performed. Enthalpies of formation, using homodesmotic reactions, were calculated and compared with experimental data. The computational Study was also extended to the isomeric compound 2,3'-bithiophene. Detailed inspections of the molecular and electronic structures of the compounds studied were carried out. Finally, bond dissociation enthalpies (BDE) and enthalpies of formation of thienyl radicals were also computed.
palavras-chave
FIELD-EFFECT TRANSISTORS; THIN-FILM TRANSISTORS; 2-AND 3-THIOPHENECARBOXYLIC ACIDS; KNUDSEN EFFUSION APPARATUS; STANDARD MOLAR ENTHALPIES; DENSITY-FUNCTIONAL THEORY; THERMODYNAMIC PROPERTIES; OPTOELECTRONIC DEVICES; SCANNING CALORIMETERS; ELECTRON-DIFFRACTION
categoria
Chemistry; Physics
autores
da Silva, MAVR; Santos, AFLOM; Gomes, JRB; Roux, MV; Temprado, M; Jimenez, P; Notario, R
nossos autores
José R. B. Gomes
Investigador Principalagradecimentos
Thanks are due to Fundacao para a Ciencia e Tecnologia (FCT), Lisbon, Portugal, and to FEDER for financial support to Centro de Investigacao em Quimica, University of Porto. A.F.L.O.M.S. and J.R.B.G. thank FCT and the European Social Fund (ESF) under the Community Support Framework (CSF) for the award of a PhD research grant (SFRH/BD/12886/2003) and a postdoc (BPD/11582/2002) research scholarship, respectively. We acknowledge the support of the Spanish MEC/DGI under projects CTQU2006-1078/BQU and CTQ2007-60895/BQU. M.T. would like to thank MEC/SEUI, FPU AP 2002-0603, Spain for financial support.