Calorimetric and Computational Study of 2- and 3-Acetyl-1-methylpyrrole Isomers

• Published in: The journal of physical chemistry. B 2010-03, Vol.114 (8), p.2846-2851
• Main Authors: Ribeiro da Silva, Manuel A. V, Santos, Ana Filipa L. O. M
• Format: Article
• Language: English
• Subjects: B: Statistical Mechanics, Thermodynamics, Medium Effects; Calorimetry; Computer Simulation; Isomerism; Models, Chemical; Pyrroles - chemistry; Quantum Theory; Thermodynamics
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp911323c

This work reports the enthalpies of formation in the condensed and gas phases of 2-acetyl-1-methylpyrrole and 3-acetyl-1-methylpyrrole, derived from the standard (p o = 0.1 MPa) molar enthalpies of combustion, in oxygen, Δc H m o, measured by static bomb combustion calorimetry and the standard molar enthalpies of vaporization, Δl g H m o, at T = 298.15 K, obtained by high-temperature Calvet microcalorimetry. The theoretically estimated gas-phase enthalpies of formation were calculated from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level; the computed values compare very well with the experimental results obtained in this work and show that the 2-acetyl-1-methylpyrrole is thermodynamically more stable than the 3-isomer. Furthermore, this composite method was also applied in the calculation of bond dissociation enthalpies, gas-phase basicities, proton and electron affinities, and adiabatic ionization enthalpies.