title: Ab Initio Highly Correlated Conformational Analysis of 1,2-Difluorethane and 1,2-Dichloroethane.
abstract: Temperature-dependent conformational population calculations for anti and gauche forms of 1,2-dichloroethane and 1,2-difluorethane were carried out at a highly correlated level of theory (MP4(SDTQ) and CCSD(T)) employing good quality basis sets (6-311++G(3df,3pd) and aug-cc-pVQZ) for the determination of gas relative conformational energies, making use of the statistical thermodynamics formalism for the evaluation of the thermal energy correction at the MP2/6-311++G(3df,3pd) and MP2/aug-cc-pVTZ levels. In addition to the standard calculation of thermodynamic partition functions, a treatment of the lowest-frequency vibrational mode as hindered rotation and anharmonic correction to vibrational frequencies was also included. We found a good agreement between ab initio calculated conformational population values and experimental gas-phase electron diffraction data for the 1,2-dicloroethane. However, for the 1,2-difluorethane species, a reasonable agreement with the experimental anti/gauche population ratio obtained from the analysis of gas-phase far-infrared (50-370 cm(-1)) and low-frequency Raman (70-300 cm(-1)) spectra was not obtained. The results reported here indicate that, for 1,2-difluorethane, and probably other substituted alkanes where the gauche effect is of relevance, a more appropriated treatment of the low-frequency modes must be pursued in order to reproduce experimental conformational population data.
authors.affiliation: Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais (UFMG), Campus Universitário, Pampulha, Belo Horizonte, MG, 31270-901, Brazil, Diretoria de Ciências Exatas (DCX), Centro Universitário do Leste de Minas Gerais, UniLeste-MG, Campus I, Coronel Fabriciano, MG, 35170-056, Brazil, and Núcleo de Estudos em Química Computacional (NEQC), Departamento de Química, ICE, Universidade Federal de Juiz de Fora (UFJF), Campus Universitário, Martelos, Juiz de Fora, MG, 36036-330, Brazil.
authors.forename: Mauro L
authors.initials: ML
authors.lastname: Franco
authors.affiliation: Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais (UFMG), Campus Universitário, Pampulha, Belo Horizonte, MG, 31270-901, Brazil, Diretoria de Ciências Exatas (DCX), Centro Universitário do Leste de Minas Gerais, UniLeste-MG, Campus I, Coronel Fabriciano, MG, 35170-056, Brazil, and Núcleo de Estudos em Química Computacional (NEQC), Departamento de Química, ICE, Universidade Federal de Juiz de Fora (UFJF), Campus Universitário, Martelos, Juiz de Fora, MG, 36036-330, Brazil.
authors.forename: Dalva E C
authors.initials: DE
authors.lastname: Ferreira
authors.affiliation: Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais (UFMG), Campus Universitário, Pampulha, Belo Horizonte, MG, 31270-901, Brazil, Diretoria de Ciências Exatas (DCX), Centro Universitário do Leste de Minas Gerais, UniLeste-MG, Campus I, Coronel Fabriciano, MG, 35170-056, Brazil, and Núcleo de Estudos em Química Computacional (NEQC), Departamento de Química, ICE, Universidade Federal de Juiz de Fora (UFJF), Campus Universitário, Martelos, Juiz de Fora, MG, 36036-330, Brazil.
authors.forename: Hélio F Dos
authors.initials: HF
authors.lastname: Santos
authors.affiliation: Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais (UFMG), Campus Universitário, Pampulha, Belo Horizonte, MG, 31270-901, Brazil, Diretoria de Ciências Exatas (DCX), Centro Universitário do Leste de Minas Gerais, UniLeste-MG, Campus I, Coronel Fabriciano, MG, 35170-056, Brazil, and Núcleo de Estudos em Química Computacional (NEQC), Departamento de Química, ICE, Universidade Federal de Juiz de Fora (UFJF), Campus Universitário, Martelos, Juiz de Fora, MG, 36036-330, Brazil.
authors.forename: Wagner B
authors.initials: WB
authors.lastname: De Almeida