Inductive and Mesomeric Effects of the [60]Fulleropyrrolidine Fragment and [60]Fullerene Sphere: A Quantitative Evaluation Based on Theory and Experiments

Inductive and mesomeric effects of the [60]fulleropyrrolidine (Pyr=C 60 ) and the [60]fullerene (C 60 ) molecular frameworks have been investigated by linear free energy relationship analyses. The electronic effects of these moieties have been studied by expressly designing [60]fulleropyrrolidine derivative 1 , which has a C–H bond α to both a carbonyl group (C–H α ) and a C 60 cage. The extent of polarization of such a bond was then used to probe electron‐withdrawing perturbation induced by the fullerene sphere. Thermodynamic measurements based on both theoretical and experimental approaches allowed the acidity of ketone 1 to be measured; this resulted in about a 1 × 10 6 ‐fold increase in acidity with respect to that of the structurally correlated acetophenone. Experimental and theoretical kinetic determinations were used to determine the stereolability of ketone 1 , which was, in fact, chiral due to the stereogenic carbon α to the carbonyl group. Also, these results confirmed the very strong tendency for the C 60 sphere to promote breaking of the C–H α bond. Thismeans that the Pyr=C 60 and C 60 fragments are able to express electron‐withdrawing effects stronger than those of halogen atoms, but less effective than those of carbonyl derivatives (e.g., ketones, carboxylic acids or acyl derivatives). Finally, the σ p , σ I and σ R – descriptors of inductive and/or mesomeric effects were successfully estimated for both Pyr=C 60 and C 60 fragments thanks to the integrated use of an original procedure based on semi‐empirical calculations and Hammett/Taft correlations involving mono‐ or dual‐parameter equations.