title: Thermochemistry of bithiophenes and thienyl radicals. A calorimetric and computational study.
abstract: 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 CO(2) (g) and H(2)SO(4) x 115 H(2)O, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The vapor pressures of these two compounds were measured as 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(o) = 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.
authors.affiliation: Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal. risilva@fc.up.pt
authors.forename: Manuel A V
authors.initials: MA
authors.lastname: Ribeiro da Silva
authors.forename: Ana Filipa L O M
authors.initials: AF
authors.lastname: Santos
authors.forename: José R B
authors.initials: JR
authors.lastname: Gomes
authors.forename: María Victoria
authors.initials: MV
authors.lastname: Roux
authors.forename: Manuel
authors.initials: M
authors.lastname: Temprado
authors.forename: Pilar
authors.initials: P
authors.lastname: Jiménez
authors.forename: Rafael
authors.initials: R
authors.lastname: Notario