Fairly recently, reactive MAO species were detected during the hydrolysis of Me3Al in polar solvent using the technique of ESI-MS. This sensitive analytical technique relies on ion-pair formation between reactive MAO species and a Lewis base donor such as (Me3SiO)2SiMe2 (OMTS). In sufficiently low amounts, OMTS reacts reversibly with MAO according to Scheme 1. During the hydrolysis process, anions with the composition [(MeAlO)n( )mMe] -(hereinafter abbreviated [n,m] -) were detected with variable intensity. Those formed most rapidly had n ≥ 7 with m = 4, of which the most intense were initially [7,4] -or [8,4] -depending on experimental conditions. Experiments in odifluorobenzene using stoichiometric Me3Al and H2O featured [7,4] -as the most intense anion. However, in fluorobenzene, at the same stoichiometry [8,4] -was the major anion detected (Figure , bottom), unless excess Me3Al was present, in which case [7,4] -was the major anion detected at short reaction times (Figure , top). At longer time scales, all mixtures evolved to form higher m/z anions of which the [16,6] -anion was most intense as is seen with commercial hydrolytic MAO (h-MAO). The preponderance of even-numbered anions (i.e. n = 14, 16, 18) at longer reaction times suggested an oligomerization mechanism involving sheet structures formed from linear MAO species. Anions with m/z ratios < 709 were present in only trace amounts during these experiments, despite the use of continuous reaction monitoring techniques. Species that were reproducibly detected include [5,3] -(M + = 521 Da) and [6,4] -(M + = 651 Da) and its hydrolyzed analogue [6,4-OH] -with m/z = M + +2 = 653 Da. In these spectra, the hydrolyzed anion was more intense than its parent ion (Supporting Information Figure S-1). The lowest molecular weight (MW) anion detected in these experiments had m/z = 465 and nominal formula [(MeAlO)4(Me3Al)3OH] -, i.e. [4,3-OH] -. Since none of these anions are detected in commercial h-MAO some may correspond to intermediates in the hydrolysis of Me3Al. Previous theoretical studies identified chains, rings, and sheets as the most stable neutral MAO structures for n ≤ 8 and m ≤ 5. Building on this foundation, we undertook a comprehensive investigation of structure-stability-reactivity relationships using a hierarchy of computational methods (DFT, MP2, and CCSD(T)) to explain the distribution of species observed in these monitoring experiments. This multi-level theoretical approach not only provided insights into the experimental observations but also revealed significant limitations in DFT's ability to accurately describe the relative stabilities of small MAO species.