Thermochemistry of 4-HOC6H4COR (R = H, CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, and n-C6H13) compounds

Abstract

The thermochemistry of 4-HOC6H4COR (R=H, CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, and n-C6H13) compounds was investigated using enthalpy of vaporization/sublimation measurements by Calvet-drop microcalorimetry and W1-F12 and CCSD(T)-F12 ab initio calculations. Based on the obtained results, standard (p°=1bar) molar enthalpies of formation in the solid, ΔfHmo(cr), and gaseous, ΔfHmo(g), states, at T=298.15K, could be derived for the complete series of compounds. An excellent linear correlation was found when the ΔfHmo(g) values were plotted as a function of the number of carbon atoms in the alkyl side chain (nc), with a CH2 increment of 21.8±0.2kJ·mol−1. Despite the differences in molecular packing between the crystalline 4-HOC6H4COR compounds, approximate additivity of their cohesive energies (as measured by the standard molar enthalpy of sublimation) with nc was also noted, the CH2 increment being 6.6±0.6kJ·mol−1.