Standard molar enthalpies of formation of methylbenzophenones

Abstract

AbstractThe standard (po = 0.1 MPa) molar enthalpies of formation of 2‐, 3‐, and 4‐methylbenzophenone were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of vaporization or sublimation of the three isomers. The standard molar enthalpies of formation of the three isomers of methylbenzophenone, in the gaseous phase and at T = 298.15 K have been derived from the corresponding standard molar enthalpies of formation in the condensed phase and standard molar enthalpies for phase transition. The results obtained are (27.2 ± 3.7) kJ · mol−1, (22.7 ± 4.0) kJ · mol−1, and (20.4 ± 3.0) kJ · mol−1 for 2‐methyl, 3‐methyl, and 4‐methylbenzophenones, respectively. Standard molar enthalpies of formation were also estimated by employing two different methodologies, one based on the Cox scheme and one other based on DFT computations. The agreement between experimental and estimated results is very good. Two possible conformations were found for the 2‐methyl and 3‐methylbenzophenones, one with the CO bond pointing in the same direction of the PhCH3 bond and another one with these bonds pointing in different directions. The former conformations are most stable by 5.1 and 0.9 kJ · mol−1 for 2‐methyl and 3‐methyl isomers, respectively. Copyright © 2007 John Wiley & Sons, Ltd.