These ASA calculations indicate that interaction energy between the two parts, rather than strain energy of each part, is the key factor for the different activation barriers to ring-opening. Further insight into these differences can be found through examination of the binding (or lack thereof) between the substrate and aluminum-based metalloligand. The computational study reveals that intermediate Int-5 of 2-methylfuran is generated from Int-3 and then undergoes the C-O bond activation by TS-3, while Int-3 of 2-methylthiophene directly leads to the C-S bond activation. In Int-5, the oxygen lone pair of 2-methylfuran coordinates to the Al 1 centre with a short O-Al 1 distance (1.93 Å). The Mayer bond order for the O-Al 1 interaction is calculated as 0.3, suggestive of a substantial O-Al 1 interaction.