The enthalpies of the reactions AnO2 + ï‚® AnO+ + O and AnO2 + + H2O ï‚® AnO2(H2O)+, and those of the isomerisation of the latter to AnO(OH)2 +, have been calculated for An = Paâ€“Pu. The data match previous experimental and computational values very closely, and the computed enthalpy for the isomerisation of PaO2(H2O)+ to PaO(OH)2 +, requested by the authors of Inorg. Chem. 2015, 54, 7474, is found to be 0.8 kJ/mol. The NPA, NBO and QTAIM approaches are used to probe covalency in the Anâ€“Oyl bond of AnO2(H2O)+, and all metrics agree that these bonds become increasingly covalent as the 5f series is crossed, providing rationalisation for the increasingly endothermic isomerisation reactions. QTAIM analysis indicates that the An=O and Anâ€“OH bonds in the oxide hydroxide isomers also become increasingly covalent as the 5f series is crossed.