Experimental and Computational Thermochemistry of 2- and 3-Thiophenecarboxylic Acids

Abstract

The enthalpies of combustion and sublimation of 2-and 3-thiophenecarboxylic acids were measured and the gas-phase enthalpies of formation at 298.15 K were determined. Standard ab initio molecular orbital calculations at the G2(MP2) and G2 levels were performed, and a theoretical study on molecular and electronic structures of the studied compounds has been carried out. Calculated enthalpies of formation using atomization and isodesmic bond separation reactions are compared with the experimental data. From experimental and theoretical results it seems that 3-thiophenecarboxylic acid is slightly more stable than the 2-isomer. A comparison of substituent effect of the carboxylic group in benzene and thiophene rings has been made.

Thermochemical study of arene carboxylic acids

“…The enthalpies of formation of the isomeric naphthoic acids have been calculated using the simple and direct homodesmotic reaction (5) naphthalene + benzoic acid → naphthoic acid + benzene (5) The calculated enthalpies of formation are collected in Table 3. Scheme 1 gives the differences found between the experimental enthalpies of formation of the arenoic acids studied and given in Table 1 and the reference compound, benzoic acid.…”

“…In this article we analyze and compare the energetics of the so-derived arenoic acids from the results of a combination of experimental determinations and high-level ab initio calculations of enthalpies of formation, ∆ f H°m which we have recently reported. [5][6][7] equipped with a rotary bomb was used.…”

“…All the results obtained for 2-and 3-thiophenecarboxylic acids, 5 2-and 3-furancarboxylic acids, 6 and 1-and 2-naphthoic acids, 7 are given in the respective references. Table 1 gives the results obtained for the enthalpies of formation in both condensed and gas states, and the sublimation enthalpies for these compounds.…”

The thermochemistry of alkanethiols and thioethers. Estimation of the enthalpies of formation of 1,3-dithiapropane and 1,3,5-trithiapentane

“…Experimental enthalpies of formation a of alkanes, alkanethiols and thioethers, used in this work, and calculated With the purpose of checking the accuracy of the estimated enthalpies of formation of the above mentioned two compounds, we have also carried out a theoretical study, calculating their enthalpies of formation at the G2(MP2), G2 and G3 levels. These methods have been previously used by us [21][22][23][24][25][26][27][28][29] for the calculation of the enthalpies of formation of different compounds containing S atoms: thiirane, 21 thiane, 21,22 1,3-and 1,4-dithiane, 21 1,3,5-trithiane, 22 2-and 3-thiophenecarboxylic acids, 23 thiane sulfoxide and thiane sulfone, 24 1,3-dithiane sulfone, 26 and 1,3-dithiane sulfoxide. 27 In all the cases, a good agreement between experimental and theoretical results was obtained.…”

Enthalpy of formation of thiophene derivatives

“…The following compounds with known experimental enthalpies of formation in the gas phase were used for this purpose [2][3][4][5][6][7][8][9][10][11][12][13]: thiophene-2-carbaldehyde (1), thiophene-3-carbaldehyde (2), 3-methylthiophene-2-carbaldehyde (3), 5-methylthiophene-2-carbaldehyde (4), 5-ethylthiophene-2-carbaldehyde (5), 2-acetylthiophene (6), 3-acetylthiophene (7), 2-acetyl-3-methylthiophene (8), 2-acetyl-4-methylthiophene (9), 2-acetyl-5-methylthiophene (10), 3-acetyl-2,5-dimethylthiophene (11), thiophene-2-carboxylic acid (12), thiophene-3-carboxylic acid (13), 3-methylthiophene-2-carboxylic acid (14), 5-methylthiophene-2-carboxylic acid (15) (Table 1), calculated by the PM3, MNDO, AM1, and MINDO methods correlate with the experimental results Δ f H 0 exp . The correlation coefficients were 0.9976, 0.9971, 0.9955, and 0.8022 respectively.…”