2- and 3-Acetylpyrroles: A Combined Calorimetric and Computational Study

Abstract

A combined experimental and computational study on the thermochemistry of 2- and 3-acetylpyrroles was performed. The enthalpies of combustion and sublimation were measured by static bomb combustion calorimetry and Knudsen effusion mass-loss technique, respectively, and the standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, were determined. Additionally, the gas-phase enthalpies of formation were estimated by G3(MP2)//B3LYP calculations, using several gas-phase working reactions, and were compared with the experimental ones. N-H bond dissociation enthalpies, gas-phase acidities and basicities, proton and electron affinities and ionization enthalpies were also calculated. Experimental and theoretical results are in good agreement and show that 2-acetylpyrrole is thermodynamically more stable than the 3-isomer. The substituent effects of the acetyl group in pyrrole, thiophene and pyridine rings were also analyzed.

Experimental and computational thermochemistry of 1-phenylpyrrole and 1-(4-methylphenyl)pyrrole

“…For each compound, the calculated enthalpies of sublimation obtained from each individual orifice are in consonance within experimental error. The equilibrium pressures at this temperature pðhTiÞ and the entropies of sublimation, at equilibrium conditions, are also presented with the later calculated as For each compound studied, the value of D g cr C p;m was assumed as being À50 J Á K À1 Á mol À1 , resembling estimations made by other authors [54], a value that our Research Group has already used for other organic compounds [30,31,[55][56][57][58][59][60][61][62]. Table 7 presents, for each compound, the values, at T = 298.15 K, of the standard molar enthalpies, entropies, and Gibbs energies of sublimation.…”

“…Previously, we have reported calorimetric and computational studies of pyrrole derivatives, namely 2-and 3-acetylpyrroles [30], 2-pyrrolecarboxylic acid and 1-methyl-2-pyrrolecarboxylic acid [31], and 2-and 3-acetyl-1-methylpyrroles [32]. As part of our thermochemical study on pyrrole derivatives and on the understanding of the enthalpic effects caused by the addition of different substituent groups in the pyrrole ring, this work presents an experimental and computational study of 1-phenylpyrrole and 1-(4-methylphenyl)pyrrole, whose structural formulae are represented in figure 1.…”

Experimental thermochemical study of 3-acetyl-2-methyl-5-phenylthiophene

“…The value of D g cr C p;m was estimated as being À50 J Á K À1 Á mol À1 , according to estimations made by Burkinshaw and Mortimer [60], a value that our Research Group has already used in previous works devoted to other organic compounds [4,9,10,13,14,[61][62][63][64]. The standard molar enthalpy, D g cr H m , entropy, D g cr S m , and Gibbs energy of sublimation, D g cr G m , at T = 298.15 K, are presented in table 6.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 16, 2005) and the discipline

“…The aim of the article by Alkorta and Elguero [148] was designed to study the influence of the carboxylic acid and its methyl ester substituents on the tautomerism of azoles using DFT calculations. While the enthalpy of formation of numerous such species have long been known, it was only in the year preceding the publication of the current review that it was measured for the parent pyrrole-2-carboxylic acid and its N-methyl derivative [152]. That of the corresponding 3-isomers remains unreported.…”