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 ${\Delta }_{\text{f}}{H}_{298\text{K}}^{°}$(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.