Computational Thermo-chemical Study of Enthalpies of formation of β-Alkylthiophenes Using Ab Initio and DFT Calculations

Abstract

The values for the standard molar enthalpies of formation of a series of the β-ring position alkyl-substituted thiophenes are calculated at 298.15 K using the Hartree-Fock (HF) and density functional theory (DFT) calculations. The results obtained are discussed in terms of the substituent effect on the structural, electronic, and energetics of the titled molecules. In the atomization energy route, the values for the standard enthalpies of formation of these compounds in the gas phase,ΔH°f ,298 , obtained using the B3LYP/6-31G(d,p) level of theory, can be successfully correlated to the substituent length via an excellent linear dependence. However, the ΔH°f ,298 (g) values (g) obtained using the HF/6-31G(d,p) level of theory are not able to predict the experimental behavior of the alkyl thiophenes (ATs). In the formation reaction route, both the DFT and HF calculations reveal the same trend for the predicted values for the standard enthalpies of formation of these compounds in the condensed phase. It could be anticipated that the proposed method can be extended to estimate the relative thermodynamic stabilities of the oligomers and polymers consisting of these building blocks.