Reactivity descriptors vs. reaction pathways in polar Diels–Alder reactions of 1-nitrocyclopentadiene: insights from MEDT

The predictive relationship between MEDT reactivity descriptors and the actual reaction pathways was investigated for the polar Diels – Alder reactions of 1-nitrocyclopentadiene with electron-deficient and electron-rich alkenes at the ωB97XD/6-311G(d) level. Global and local Conceptual DFT (CDFT) indices were used to anticipate the polar character and regioselectivity of the cycloadditions, while Global Electron Density Transfer (GEDT) values quantified the magnitude and direction of charge transfer at the transition states. The explored reaction pathways (energetical and geometrical description of all critical points) were subsequently analyzed and compared with these predictions. The results show that the electronic role of 1-nitrocyclopentadiene strongly depends on the nature of the reaction partner, leading to either normal or reverse electron density flux. The ordering of transition states, degree of asynchronicity, and relative orientation of molecular segments are con-sistent with the polarity predicted by CDFT indices and confirmed by GEDT analysis. Complementary ELF and BET studies reveal the detailed topological evolution of bonding and explain the origin of the observed asynchronous but single-step mechanisms. Overall, the combined analysis demonstrates a clear correspondence between reactivity descriptors and the computed reaction pathways, supporting the reliability of the MEDT framework for rationalising polar Diels – Alder reactivity.