G. Van De Woude

REACTIVITY OF FULLERENES. QUANTUM-CHEMICAL DESCRIPTORS VERSUS CURVATURE

Abstract The relation between the reactivity of a fullerene towards a nucleophile and the curvature of the fullerene surface, reflecting the hybridisation of the carbon atoms, is investigated. Model 3-21G calculations on distorted ethenes show that the electronic part of the molecular electrostatic potential, V el , might be a good measure for the reactivity of a double bond towards a nucleophile when only the influence of geometrical changes is considered (increasing reactivity upon increasing curvature). STO-3G calculations on the fullerenes C 60 , C 70 and C 76 again indicate the quality of V el as a reactivity descriptor. Both the regioselectivity in C 60 , C 70 and C 76 (in line with local curvature), and the relative reactivity of C 60 and C 70 calculated by V el are in agreement with experimental data. The local hardness for these systems shows a fair correlation with the global hardness calculated in a finite difference approximation.

Local softness and hardness as reactivity indices in the fullerenes C24C76

Abstract The condensed local softness, s k + or condensed fukui function, f k + , approximated by Mulliken atomic charge differences, are used as a descriptor of the regioselectivity for the fullerenes (from C 24 to C 76 ) towards a nucleophilic attack. In general the results, which are in agreement with experimental data, can be interpreted in terms of a pyramidalization angle effect, soft-hard alternations and softness delocalization. The local hardness on the most reactive carbon atom in each fullerene turns out to be a valuable descriptor of the intermolecular reactivity sequence. The maximal hardness principle is used to discuss the stability for the larger fullerenes (C 50 , C 60 , C 70 and C 76 ). The calculated hardness, approximately calculated as the LUMO-HOMO energy difference, confirms the fact that C 60 and C 70 are the most stable fullerenes.

An ab initio quantum chemical study on the structure, stability and polymerization of C28 and its derivatives

Abstract STO-3G calculated reaction energies of the radical reactions producing C 28 H n ( n = 1, 2, 3, 4) from the unstable C 28 are used to discuss the stabilization of these derivatives. The influence of the nature of various groups X (X is F, OH, NH 2 , CI, CH 3 , i Pr, CN, CF 3 and t Bu) on the stabilization of C 28 is investigated using the isodesmic reactions in which one or more hydrogens of C 28 H 4 are substituted by X. In general, all our calculations predict that C 28 is stabilized by the addition of hard monovalent atoms (or groups) such as H and F on the four dangling bonds. When applying the Hard and Soft Acids and Bases (HSAB) principle to these isodesmic reactions, C 28 H 3 is predicted to be harder than CH 3 . The stability of C 28 H 3 and the localization of its unpaired electron suggest that this molecule may be used as a monomer in a radical polymerization. The stability analysis of the dimer, trimer, tetramer and pentamer (in linear or branched form) shows that these molecules are stable with strong C 28 C 28 bonds.