Comparative density functional theory study on the relative gas phase enthalpies and free energies of formation for the mono- through hepta-halogenated (X=F, Cl, Br) anthraquinones

Gas phase standard state (298.15 K, 1 atmosphere) relative enthalpies and free energies of formation were calculated for all mono- through hepta-halogenated (X=F, Cl, Br) anthraquinone congeners using the B3LYP, BHandHLYP, M062X, PBE0, and B97D density functionals with the 6-311++G(d,p) basis set. All levels of theory yielded similar results with strong intra- and inter-method correlations for both the relative enthalpy and free energy values and the corresponding thermodynamic stability rank. Within each homolog group, the most thermodynamically stable isomers are those which maximize substitution at the lateral positions (2, 3, 7, and 8) versus the less stabilizing peri positions (1, 4, 6, and 9), while also minimizing destabilizing adjacent substitution patterns (1/2, 2/3, 3/4, 6/7, 7/8, and 8/9). These trends are consistent regardless of halogen substituent or theoretical method employed, and are analogous to those predicted for other classes of halogenated ortho-diaryl systems with single connecting atoms