Addition of Aryl and Fluoroalkyl Radicals to Fullerene C₇₀:  ESR Detection of Five Regioisomeric Adducts and Density Functional Calculations

Abstract

The addition of several photochemically generated aryl and fluoroalkyl radicals to fullerene C 70 was studied by electron spin resonance and the results were compared with those obtained with C 60 . While simple alkyl radicals afford only three of the five expected RC 70 • regioisomers, the more reactive aryl and fluoroalkyl radicals give rise to four, except for the trifluoromethyl radical which yielded for the first time the ESR spectra of all five expected isomers. Semiempirical MO calculations and density functional theory calculations were carried out for HC 60 • and for the five HC 70 • regioisomers as models for the corresponding alkyl, aryl, and fluoroalkyl analogs in order to describe the unpaired electron distribution in these radical species and as an aid in the assignment of the observed spectra to specific RC 70 • regioisomers.

Radical reactions of C60Ph5Cl: EPR study and DFT calculations

“…This affords the opportunity to use radical phosphorylation as a model for determination of the regiochemistry of the addition of free radicals to nearly symmetrical fullerene derivatives. It follows from the previous contributions [1,5,7], that radical addition to fullerenes depends either on thermodynamic stability of the adducts formed or the convexity of the starting molecule, i.e. the more thermodynamically stable this is, the more easily it will be attacked by the radical products.…”

“…Because of the size of the molecules, we used semi-empirical molecular orbital theory to optimize the geometry, as it was done in the study of Å C 70 H [5] and radicalanions of mono-and bis-(trans-1-fulleropyrrolidines) [14]. The calculations were done with the MNDO Hamiltonian with the PM3 parametrization at the ROHF level.…”

“…In previous studies of hfc constants and density distributions in fullerenes and their derivatives, other authors [5,11,14] used both semi-empirical and DFT methods. For studying of the products of the reaction of Å OH with watersoluble C 60 [C(COOH) 2 ] n (n ¼ 2-6) the authors used semi-empirical molecular orbital (AM1 and PM3) calculations and Huckel molecular orbital theory [11].…”

“…For studying of the products of the reaction of Å OH with watersoluble C 60 [C(COOH) 2 ] n (n ¼ 2-6) the authors used semi-empirical molecular orbital (AM1 and PM3) calculations and Huckel molecular orbital theory [11]. For the study of Å C 70 H the authors used an unrestricted spin formalism at the nonlocal (gradient-corrected) level with the non-local exchange potential of Becke together with the nonlocal correlation functional of Perdew [5]. For studying of the radical-anions of mono-and bis-(trans-1-fulleropyrrolidines) the authors used the ab initio (STO-3G) level and DFT B3LYP approach with a 6-31G(d) basis set [14].…”

“…It was found by EPR that in case of addition to C 60 where all the carbons are equivalent, only one type of fullerenyl radicals form [3,4]. C 70 contains five types of non-equivalent carbon atoms with different reactivity, and here the number of the adducts formed varies from three to five depending on the nature of the radicals added [5,6]. There are 19 types of non-equivalent carbon atoms in fullerene C 76 , which seem each to have different reactivities toward radicals [1,7].…”