Experimental and Computational Study on the Molecular Energetics of 2-Pyrrolecarboxylic Acid and 1-Methyl-2-pyrrolecarboxylic Acid

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2009-09, Vol.113 (35), p.9741-9750
• Main Authors: Santos, Ana Filipa L. O. M, Silva, Manuel A. V. Ribeiro da
• Format: Article
• Language: English
• Subjects: A: Molecular Structure, Quantum Chemistry, General Theory; Calorimetry; Carboxylic Acids - chemistry; Computer Simulation; Gases - chemistry; Models, Molecular; Molecular Conformation; Phase Transition; Proline - analogs & derivatives; Proline - chemistry; Pyrroles - chemistry; Thermodynamics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp905375h

This paper reports a combined thermochemical experimental and computational study of 2-pyrrolecarboxylic acid and 1-methyl-2-pyrrolecarboxylic acid. Static bomb combustion calorimetry and Knudsen mass-loss effusion technique were used to determine the standard (p° = 0.1 MPa) molar enthalpies of combustion, Δc H m °, and sublimation, Δcr g H m °, respectively, from which the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, were derived. The values obtained were −(286.3 ± 1.7) and −(291.6 ± 1.7) kJ·mol for 2-pyrrolecarboxylic acid and 1-methyl-2-pyrrolecarboxylic acid, respectively. For comparison purposes, the gas-phase enthalpies of formation of these two compounds were estimated by G3(MP2)//B3LYP and MP2 approaches, using a set of gas-phase working reactions; the results are in excellent agreement with experimental data. G3(MP2)//B3LYP computations were also extended to the calculation of N−H bond dissociation enthalpies, gas-phase acidities and basicities, proton and electron affinities and adiabatic ionization enthalpies. Moreover, the results are also discussed in terms of the energetic effects of the addition of a carboxylic and of a methyl groups to the pyrrole ring and compared with structurally similar compounds.