Theoretical study on the acidity behavior of some N-methylpyrazole derivatives: CBS-Q method and United Atom (UA) molecular cavity effect

In this paper, the acidity behavior of some methyl and bromine substituted N-methylpyrazoles have been studied theoretically by using the CBS-Q calculation method. The three United Atom molecular cavity models (UAHF, UAKS and UAO) with the IEFPCM method and two thermodynamic cycles have been used for acidity calculations. The relationship between the experimental acidity constants and the theoretical results were searched by using a correlation coefficient, mean absolute error and acidity order for understanding the acidity behavior. The most fit calculated pKa values to experimental acidity have been found with UAHF and UAKS radii. But the theoretical acidity order with UAKS radii has been found almost the same with experimental acidity order. The best correlation has been observed between proton affinity (PA) and experimental acidity values also.