بخشی از متن دانلود فایل مقاله Prediction of accurate pKa values of some ?-substituted carboxylic acids with low cost of computational methods :
سال انتشار : 2015
تعداد صفحات :22
The acidity constants (pKa) of thirty four (34) ;-substituted carboxylic acids in aqueous solution havebeen calculated using conductor-like polarizable continuum (C-PCM) solvation model. The gasphaseenergies at the Density Functional Theory (DFT-MPW1PW91) and solvation energies atHartree Fock (HF) are combined to estimate the pKa values which are very close to the experimentalvalues where, and the root-mean-square error (rmse) is less than 0.9. In addition, the pKa valuespredicted by Multilinear Regression (MLR), Principle Components Regression (PCR) and PartialLeast Square Regression (PLSR) methods showed an excellent correlation to the experimental valueswhere the root-mean-square error (rmse) decreases from 0.9 to 0.293, 0.326 and 0.319 respectively.Furthermore, the rmse of pKa values found less than 0.3 when the solvation models of some powerfulelectron withdrawing substituted acids are employed at the level of MPW1PW91 theory. Thecomputation by different regression methods showed reasonably a better calculation of pKa valuesthrough the lower root-mean-square errors (rmse).