Energetics and Molecular Structure of 2,5-Dimethyl-1-phenylpyrrole and 2,5-Dimethyl-1-(4-nitrophenyl)pyrrole

Abstract

Thermochemical and thermodynamic properties of 2,5-dimethyl-1-phenylpyrrole and 2,5-dimethyl-1-(4-nitrophenyl)pyrrole have been determined by using a combination of calorimetric and effusion techniques as well as high-level ab initio molecular orbital calculations. The standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline state, Δ(f)H(m)°(cr), at T = 298.15 K, were derived from the standard molar enthalpies of combustion, Δ(c)H(m)°, which were obtained from static bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies of sublimation, Δ(cr)(g)H(m)°, at T = 298.15 K. From the experimental results, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, were derived. The results were analyzed and interpreted in terms of enthalpic increments and molecular structure. For comparison purposes, standard ab initio molecular calculations at the G3(MP2)//B3LYP level were performed, using a set of working reactions and the gas-phase enthalpies of formation of both compounds were estimated; the results are in excellent agreement with experimental data. The computational study was also extended to the determination of proton and electron affinities, basicities and adiabatic ionization enthalpies.

Energetics of 1-(aminophenyl)pyrroles: A joint calorimetric and computational study

“…As was already noticed for 1-phenylpyrrole and derivatives, [5][6][7][8] the steric repulsions between the H of the a-C of pyrrole ring and the H (in the case of the 3-and 4-isomers), or the -NH 2 group (for the 2-isomer) of the phenyl ring at the ortho position, are minimum when these three isomers take a twist orientation with dihedral angles between the phenyl and pyrrole planes of 52.3°for 1-(2-aminophenyl)pyrrole, 36.6°for 1-(3-aminophenyl)pyrrole, and 41.1°for 1-(4-aminophenyl)pyrrole. The phenyl/pyrrole dihedral angle is higher in the 2-isomer due to the steric interactions caused by the proximity of the amino group and the hydrogen atom of the C10 of the pyrrole ring.…”

“…By fitting the experimental data to the integrated form of this equation, ln(p/Pa) = a À b Á (T/K) À1 , the standard molar enthalpy of sublimation of 1-(2-aminophenyl)pyrrole, at the mean temperature of For 1-(2-aminophenyl)pyrrole, the value of D g cr C p;m considered was À50 J Á K À1 Á mol À1 [34], a value that has already been used in previous papers of other pyrrole derivatives [1,[3][4][5][6][7][8]. 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 5.…”

“…Among these nitrogen heterocyclic compounds studied are acetylpyrroles and their derivatives [1][2][3], pyrrolecarboxylic acids [4], and phenylpyrrole derivatives [5][6][7][8]. Following the same line of investigation, we have studied now the energetics of (aminophenyl)pyrroles, whose structural formulae are depicted in figure 1.…”

Molecular Energetics of Alkyl Pyrrolecarboxylates: Calorimetric and Computational Study

“…Following our studies on the thermodynamic and thermochemical properties of several substituted pyrroles and their relationship with the corresponding molecular structures, − which are intended to be used as a building blocks of porphyrins, polypyrroles, and drugs with high therapeutical potential, we report, in the present work, an experimental and computational study on the energetic and structural properties of several alkyl pyrrolecarboxylates (alkyl = methyl or ethyl). It is of great importance for the understanding of the activity and behavior of large molecules to know the molecular energetics of its fragments.…”

Energetics and molecular structure of alkyl 1-methylpyrrolecarboxylates (alkyl=methyl or ethyl)

“…Experimental and computational thermodynamic studies of pyrrole derivatives, with different substituent groups [1][2][3][4][5][6][7][8][9][10][11][12][13], have been developed in our Research Group during the last few years, with the main goal to correlate the effects of the corresponding molecular structures on the energetic characteristics of the compounds. Pyrrole moiety is the structural core of the naturallyoccurring porphyrins, the tetrapyrrolic ''pigments of life'', which include the hemoglobin, porphyrins, corrins, vitamin B 12 , the bile pigments and chlorophyll, playing an important role in respiration and photosynthesis processes [14][15][16][17][18].…”