The enthalpies of formation of brominated benzenes and phenols: A theoretical prediction

The enthalpies of formation of brominated benzenes and phenols were predicted using Gaussian-4 (G4), G3X, and G3XMP2 model chemistries and a few popular density functional methods, coupled with homodesmic reactions (HR1), (HR2) in which C6H6, C6H5Br, and C6H5OH are used as reference compounds. The results from G4, G3X, and G3XMP2 agree closely within 2 kJ/mol for all brominated benzenes and phenols; while the results from density functional methods are systematically higher than the G4 ones. The predicted enthalpies of formation for 2- and 4-bromophenols are in close agreement with the recent experimental measurements. Three reactions (R1), (R2), (R3) were also used to derive ΔfH298K°(g, C6H5Br) = 98.7 ± 1.0 kJ/mol by using CH4, CH3Br, CH2Br2, CH2CHBr, and C6H6 as reference compounds at G4 and G3X levels. The value is significantly lower than the only experimental value of 105.4 kJ/mol given by Cox and Pilcher in 1970, and a re-determination is called.