A theoretical HSAB study of the acidity of carbon acids CH3Z

Abstract

A acidez em fase gasosa de nove ácidos carbonados do tipo CH 3 Z (nitrometano, acetofenona, dimetilsulfona, acetaldeído, butanona, acetona, acetato de metila, acetonitrila e dimetilsulfóxido ) foi estudada, em busca de correlações com propriedades locais e globais, calculadas em níveis 3-21G, 6-31G* e 6-31+G(3df,2p), segundo a teoria de ácidos e bases duros e macios ("HSAB"). Uma correlação razoável foi obtida com as energias de deprotonação calculadas, o que permitiu estimar a acidez em fase gasosa do tioacetato de metila (∆G o = 1476 kJ mol -1 ), próxima da do nitrometano, o membro mais ácido da série. As funções de Fukui para ataque nucleofílico dos centros aniônicos duros e macios em cada base -CH 2 Z foram usadas para interpretar as variações de acidez quando os ácidos são transferidos da fase gasosa para a fase aquosa.The gas-phase acidity of nine carbon acids of the form CH 3 Z (nitromethane, acetophenone, dimethylsulfone, acetaldehyde, butanone, acetone, methyl acetate, acetonitrile and dimethylsulfoxide) was investigated, in the search of correlations with global and local HSAB properties, calculated at the 3-21G, 6-31G* and 6-31+G(3df,2p) levels. A reasonable correlation was obtained with the calculated ionization energies. Based on the obtained correlation, the gasphase acidity of methyl thioacetate was estimated (∆G o = 1476 kJ mol -1 ) as close to that of the most acidic member of the series, nitromethane. The nucleophilic Fukui functions of the hard and soft anionic centers in each base -CH 2 Z stabilized by direct conjugation were calculated, following two different approaches, and their ratios utilized to interpret the shifts in acidity when the acids are transferred from gas-phase to aqueous solution.

On the NH and CH acidities of toluidine isomers: theoretical description and practical consequences for the synthesis of certain aniline dyes

“…For example, the acidity constant of the positively charged anilinium ion p K a ( ANH 3 + ) in DMSO is 3.8 26,29 . Aniline is also a weak acid that can only be deprotonated by very strong bases (eg, lithium organyl compounds) 30‐32 . The experimental p K a for the heterolytic dissociation of aniline to the deprotonated anion ( ANH − ) in DMSO is 30.6 14 .…”

A Theoretical Study on the Stability, Reactivity and Protonic Affinity of 2-Phenylbenzothiazole Derivatives

“…Polarized Continuum Model (PCM) [31] is taken as a solvation model. Previous theoretical work on prediction of acidity has shown that hybrid functionals such as B3LYP associated with bases 6-31+G (d, p), 6-311+G (d) and 6-311+G (3df, 3pd) lead to results in good agreement with experimental data [32][33][34]. Protonic affinities and basicity were therefore determined from geometry optimization at the B3LYP/6-31+G (d, p) theory level.…”

Relative solvation and strength of polycyano‐ and polynitromethanes in water: a study with molecular dynamics simulations

“…1,13 This may be the result of the linear correlations which are sometimes obtained between gas-phase and solvent acidities of families of organic acids. 14 Thus, we have been successful in describing the acidity of carbon acids, and not only in the gas phase 15 but also in solution, 16 in terms of theoretical descriptors, without including solvent perturbations in the calculations. The same treatment has been successfully applied by us in describing the basicity of carbonyl compounds in CCl 4 .…”