Electrocyclic ring opening (ERO) reactions of 2-pyrone, 2-pyranol and pyran and their fluoro compounds (1-6) have been studied at MP2/6-31G(𝑑) level with special emphasis on the influence of fluorine on these pericyclic/pseudopericyclic processes. Calculations clearly predict that substitution of fluorine at C6 favour the reaction both kinetically and thermodynamically. Magnetic susceptibility anisotropy ($\Delta_{\chi\text{aniso}}$), NICS(0), NBO and bond critical property (BCP) analyses clearly illustrate the following; 2-pyrone (1) and 6-fluoro-2-pyrone (2) reactions are pseudopericyclic; 6-fluoro-2-pyranol (reaction 4) corresponds to a borderline case; 2-pyranol (3) and pyran (5) and 6-fluoro pyran (6) reactions are clearly pericyclic in character. Correspondingly pseudeopericyclic reactions show up orbital disconnections and fluorine delays the occurrence of orbital disconnections on the reaction trajectory.

The competition between the two electron donors (–OCH₃ and –OSiH₃) have been studied by positioning them at geminal and vicinal locations. We have also studied the cis and trans geometrical isomerism at the vicinal location. Thermodynamic and activation parameters such as free energies have been computed to understand the potential energy surface of the reaction. Our computed activation hardness supports the proposed torquoselectivity. Further, Nucleus Independent Chemical Shift (NICS) was calculated at the ring centre of the transition state (TS) which additionally supports the torquoselectivity. The delicate preferences for the pathways have been substantiated through NBO interactions.