Determination modified enthalpy of formation of straight alkyl-chained carboxylic acids and esters

A test set of 35 straight alkyl-chained carboxylic acids and esters was examined to elucidate theoretically their enthalpies of formation by performing density-functional theory (DFT) and ab initio calculations. The calculated error for the straight structure monotonically increases with the number of methylene groups in the main alkyl chain. All calculated data were modified using a three-parameter calibration equation and the least-squares approach, to determine accurate enthalpies of formation (ΔHf). This work studied that the atomization energies of all compounds exhibited an average absolute relative error of 0.03%, and a ΔHf with a mean absolute error (M.|AE|) of just 3.1 kJ/mol (0.7 kcal/mol), according to DFT calculations.