Abstract
The values for the standard molar enthalpies of formation of a series of the B-ring position alkyl-substituted thiophenes are calculated at 298.15 K using the Hartree-Fock (HF) and density functional theory (DFT) techniques. The results obtained are discussed in term of the substituent effect on the structural, electronic, and energetics of the titled molecules. The alkyl substitution with electron donating plays a fine-tune effect on the geometries, electronics, and energetics of the species. In the atomization energy route, the standard enthalpies of formation in the gas-phase, DHº(f,298)(g), obtained using the B3LYP/6-31G(d,p) method, can be successfully correlated to the substituent length via a linear dependence. However, DHº(f,298)(g), obtained using the HF/6-31G(d,p) method, is not able to predict their experimental behavior. In the formation reaction route, both the DFT and HF calculations reveal the same trend for predicting the values for the standard enthalpies of formation in the condensed-phase. It could be anticipated that the calculations can be extended to estimate the relative thermodynamic stabilities of oligo- and polymers consisting of this building blocks.
Highlights
During the past decade, the thiophene-based compounds have been extensively used in modern drug design, biochemistry, opto-electronic devices, and electrically conductive polymers
The influence of alkyl substituents on the structure-energetics of β-alkylthiophenes was investigated by means of the two different density functional theory (DFT) and HF computational studies
Comparison of the available experimental ΔH°f,298(g) values for alkyl thiophenes (ATs) with those calculated in the atomization energy route showed that the B3LYP/6-31G(d,p) level of theory can establish linear correlations of ΔH°f,298(g) with the number of carbon atoms in the alkyl group
Summary
The thiophene-based compounds have been extensively used in modern drug design, biochemistry, opto-electronic devices, and electrically conductive polymers Their applications have received a great deal of attention from both the academic and industrial research centers.[1,2,3,4] The ease in the chemical modification of the structures of these materials can potentially allow us to fine-tune their optical and electronic properties.[5,6,7,8,9] These properties strongly depend upon the degree of the electronic delocalization present in such materials, effective conjugated length, and introduction of substituents at specific positions. The absolute enthalpies were obtained at 298.15 K and 1.0 atm by considering the corresponding thermal calculations obtained from the calculated harmonic vibrational frequencies
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