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_o
= 1 bar) molar enthalpies of formation in the solid, Δ_fH^o_m(cr), and gaseous, Δ_fH^o_m(g), states, at T = 298.15 K, could be derived for the complete series of compounds. An excellent linear correlation was found when the Δ_fH^o_m(g) values were plotted as a function of the number of carbon atoms in the alkyl side chain (n_c), with a CH₂ increment of 21.8 ± 0.2 kJmol^-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 n_c was also noted, the CH₂ increment being 6.6 ± 0.6 kJmol^-1.

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