Gas-Phase Acidities of Nitrated Azoles as Determined by the Extended Kinetic Method and Computations

作者：Nichols Charles M; Old William M; Lineberger W Carl; Bierbaum Veronica M^*

来源：Journal of Physical Chemistry A, 2015, 119(2): 395-402.

DOI：10.1021/jp5110533

Making use of the extended kinetic method and the alternative method for data analysis, we have experimentally determined Delta H degrees(acid) (kcal/mol) for six mononitrated azole species (2-nitropyrrole = 337.0, 3-nitropyrrole = 335.8, 3-nitropyrazole = 330.5, 4-nitropyrazole = 329.5, 2-nitroimidazole = 327.4, and 4-nitroimidazole = 325.0). We report an absolute uncertainty of +/- 2.2 kcal/mol that arises from the uncertainties of the reference acids; the relative values are known within 0.4 kcal/mol. Combining these experimental Delta H degrees(acid) values with Delta S degrees(acid) values calculated at the B3LYP/aug-cc-pVTZ level of theory, we report Delta G degrees(acid) (kcal/mol) for the nitroazoles (2-nitropyrrole = 329.4, 3-nitropyrrole = 328.4, 3-nitropyrazole = 323.1, 4-nitropyrazole = 322.0, 2-nitroimidazole = 319.7, and 4-nitroimidazole = 317.6); the absolute uncertainties are +/- 2.4 kcal/mol. In addition to the experimental studies, we have computationally investigated the gas-phase acidities and electron affinities of the azoles in this work, as well as higher-order aza- and dinitro-substituted azoles. We discuss trends in the stabilities of the deprotonated azoles based on aza substitution and nitro group placement. 4-Nitroimidazole has already found use as the anionic component in ionic liquids, and we propose that the additional nitrated azolate ions are potential candidates for the anionic component of ionic liquids.

• 出版日期2015-1-15