Calorimetric study of 2′-methylacetophenone and 4′-methylacetophenone

Highlights: ► Combustion calorimetry was used to determine ΔfHm∘(l) of 2′-methylacetophenone and 4′-methylacetophenone. ► Enthalpies of vaporization of 2′- and 4′-methylacetophenones were determined by Calvet microcalorimetry. ► Gas-phase ΔfHm∘ of the studied compounds have been derived. ► ΔfHm∘ (3′-methylacetophenone, g) was estimated from isomerization schemes. - Abstract: Values of the condensed phase standard (p = 0.1 MPa) molar enthalpy of formation for 2′- and 4′-methylacetophenones were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The values of the standard molar enthalpy of vaporization, at T = 298.15 K, were measured by Calvet microcalorimetry. Combining these two values, the following enthalpies of formation in the gas phase, at T = 298.15 K, were then derived: 2′-methylacetophenone, –(115.7 ± 2.4) kJ · mol−1, and 4′-methylacetophenone, –(122.6 ± 2.4) kJ · mol−1. Substituent effects are discussed in terms of stability and compared with other similar compounds. The value of the standard molar enthalpy of formation for 3′-methylacetophenone was estimated from isomerization schemes.