Resumo

RIVAS, Carlos F; NUNEZ, Jesús  e  MARQUEZ, Edgar. Theoretical prediction of substituent constant hammett using electrophilicity index. Saber [online]. 2013, vol.25, n.4, pp.445-448. ISSN 1315-0162.

Electrophilicity index (ω) is a global descriptor to estimate experimental parameters. The model molecule used was β-phenylvinyl alcohol, substituted in para by 40 functional groups. The values of ω for the derivatives were calculated by using a Density Functional Theory (DFT) method of B3LYP/6-31G *, B3LYP/6-311G * and B3LYP/6-311G ** with Gaussian’03 program. Electrophilicity was calculated using the frontier orbitals HOMO and LUMO. Plotting of σ vs. ω, showed a low linear correlation with a regression coefficient of R² = 0.54. A better correlation was found with a second-degree polynomial fit, but the R² was 0.82. The low correlation is due to the Hammett substituent constants (σ) were determined in a polar medium (eg H2O/CH3CH2OH), which contains the electronic effect and the polarization to the environment. When the substituents were reduced to 25, the correlation improved significantly (R ² = 0.99) and allows to obtain the equation σω = -0.88ω2 + 3.52ω - 3.07; where σω represents the pure electronic contribution of Hammett substituent constant.

Palavras-chave : Computational chemistry.

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