Estudos teoricos de modelos de eletronegatividade para intensidades vibracionais

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

The atomic polar tensors of a set of 12 halomethanes were calculated using ab initio wave functions with and without inclusion of electron correlation at the MP2 leveI with 6-31G(d,p) and 6-311++G(3d,3p) basis sets. The inclusion of electron correlation at the MP2 leveI is an important factor for determining the accuracy of the atomic polar tensors. The ab initio calculated mean dipole derivatives for the halomethanes molecules are highIy correlated with partial atomic charges calculated by the charge equilibration method. The charge-charge flux-overlap analysis of the atomic polar tensors for the carbons atoms in fluoromethanes and cloromethanes (including CH4) show that this correlation is determined by charge and charge flux components, respectively. The CCFO components show a strong basis set dependency, specially for the cloromethane molecules. As such the reliability of the CCFO procedure is compromised by basis set dependency, and careful use of the CCFO procedure for infrared intensities interpretation is recommended. The interpretation of mean dipole derivative as a measure of atomic charge is appropriate considering the good correlation between this invariant and atomic charges derived from atomic electronegativities. The effective charges and mean dipole derivatives for terminal atoms in the halomethanes, calculated with MP2/6-311 ++G(3d,3p) are highIy transferable and directly related to their atomic electronegativities. For carbon atoms there is an excellent linear correlation of effective charges calculated with MP2/6-311++G(3d,3p) and the terminal atom mean electronegativities. These results were used to test a previously formulated model for semiquantitative prevision of intensities sums from atomic electronegativities. The charge equilibration method was used for the calculation of atomic charges and atomic polar tensors for a set of halomethanes and diatomic molecules. Most of lhe dipole derivative signs match with the experimentally derived ones. The mean dipole derivative and effective charges calculated by the charge equilibration method for the carbon in halomethanes are linearly correlated with respective experimental values. The calculated atomic charges for terminal atoms in the halomethanes using the charge equilibration method show better agreement with experimentally derived values than the charges calculated by Sanderson s electronegativity equalization procedure.

ASSUNTO(S)

calculo tensorial metano vibração eletronegatividade

ACESSO AO ARTIGO

Documentos Relacionados