The XB interaction between X and O, as presented in Tables and, was in agreement with both the QTAIM and NBO methods and provided further validation for the previously discussed concepts related to the XB-donor and substituent effects. In relation to CAT6, it 13: LMO-EDA energy partition terms for the interaction between indole and the O-and π-type activated trans-crotonophenone under the I 2 catalysed TS1 of the Michael addition reaction (A). LMO-EDA energy partition terms for the stabilisation interaction between indole and the O-and π-type activated trans-crotonophenone under the I 2 and CAT4 catalysed TS1 of the Michael addition reaction (B and C). of the Michael addition reaction (as depicted in Figures and). Nevertheless, the trend derived for the XB-interactions, quantified using methods namely QTAIM and NBO, aligns with experimental findings, 42 where CAT1 < CAT2 < CAT3 < CAT5 < CAT6. Furthermore, the interaction between X and O atoms in the activated O-and π-type activated systems was quantified and compared. The results revealed that in the bidentate catalytic systems CAT3, CAT6, and CAT7, the E(2) and ρ BCP between the O and the X was enhanced in the π-type activation mode (Figure and Figure ). For a complete and detailed version of Figure , please refer to the supplementary information, Table . In contrast, for I 2 , E (2) and ρ BCP exhibited an overall increase in the π-type activated system, resembling a slight covalent nature, while the opposite was observed for CAT4, which had an increase in CT and ρ BCP within the O-activated mode (Figure and Figure ). The bidentate XB-based organocatalysts exhibit a clear preference for the π-type activation mode substrate, i.e., the carbonyl oxygen and the α-carbon. On the other hand, the preference trends observed for the monodentate catalysts can be attributed primarily to the nature of the binding interaction. Monodentate I 2 and CAT4 can only interact with the substrate through carbonyl oxygen or the α-carbon. The stronger non-covalent interaction between CAT4 and the carbonyl oxygen (as reflected in Figure and Figure ) relative to the interaction with the α-carbon results in the energetic preference for the O-activation mode.