Possible precursors to these anions are related to each other, and possibly to other MAO species in this size range. Figure illustrates these relationships. For example, 4,4-OH has a 4-C sheet structure and serves as a precursor to the [4,3-OH] -anion through cleavage of the Me2Al + group (highlighted in blue, Figure ). The 4,4-OH sheet is related to the 4-C 5,4 sheet through the reaction of the OH group with Me3Al and the rearrangement of the highlighted Me2Al group. This 5,4 sheet can also serve as a precursor to the [5,3] -anion, though it is not the thermodynamically most favorable neutral structure (Table ). The 6,4 4-C sheet is a possible precursor to the [6,4] -anion. It is related to the 5,4 4-C sheet through the net addition of MeAlO (Al highlighted in green, Figure ). However, for this composition, the ring structure is thermodynamically preferred over the sheet.