Theoretical Study of Diels−Alder Cycloadditions of Butadiene to C₇₀. An Insight into the Chemical Reactivity of C₇₀ as Compared to C₆₀

Abstract

The eight unique Diels-Alder cycloadditions of butadiene to C 70 are analyzed theoretically and compared with the well-established, two possible Diels-Alder cycloadditions of butadiene to C 60 . Full geometry optimizations of reactants, adducts, and transition states are performed using the AM1 semiempirical method followed by single-point ab initio energy calculations. The results show that the cycloaddition of butadiene to the C 70 fullerene in the gas phase is slightly more reactive than that to C 60 . However, in toluene solution calculations yield that the different solvent effects on C 60 and C 70 cause a significant decrease of the energy barrier in the C 60 cycloaddition, thus predicting a larger reactivity for C 60 as compared to the C 70 fullerene.

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

“…We used this semiempirical method instead of a more accurate ab initio method to compute the geometries for several reasons: first, the sizes of some of the systems studied prevented the use of ab initio molecular quantum-mechanical methods to perform optimizations, second, we have found by comparison with our previous results for C 6 H 6 , C 10 H 8 , and C 14 H 8 [73] that differences in HOMA, NICS, and PDI indices computed at the HF/6-31G* (HOMA and PDI) and HF/6-31 G* (NICS) levels by use either of the B3LYP/6-31G* or of the AM1 geometries are generally small, and third, the AM1 method yields reliable results for the geometries of C 60 , [87,88] C 70 , [88] and also for the series of PAHs studied. We used this semiempirical method instead of a more accurate ab initio method to compute the geometries for several reasons: first, the sizes of some of the systems studied prevented the use of ab initio molecular quantum-mechanical methods to perform optimizations, second, we have found by comparison with our previous results for C 6 H 6 , C 10 H 8 , and C 14 H 8 [73] that differences in HOMA, NICS, and PDI indices computed at the HF/6-31G* (HOMA and PDI) and HF/6-31 G* (NICS) levels by use either of the B3LYP/6-31G* or of the AM1 geometries are generally small, and third, the AM1 method yields reliable results for the geometries of C 60 , [87,88] C 70 , [88] and also for the series of PAHs studied.…”

Analysis of electronic delocalization in buckminsterfullerene (C60)

“…We have used the Austin model 1 (AM1) semiempirical method 44 as implemented in Gaussian 98 45 to perform geometry optimizations within the restricted formalism. We previously showed that the AM1 method yields reliable results for the geometries of C 60 46, 47 and C 70 47. Calculations of delocalization indices have been carried out using the ab initio Hartree–Fock (HF) method with the 6‐31G* basis set 48–50 at the AM1‐optimized geometries (HF/6‐31G*//AM1) by means of the AIMPAC collection of programs 51.…”

Microwave Irradiation: An Important Tool to Functionalize Fullerenes and Carbon Nanotubes

“…1), with the most reactive being the 1-2 and 5-6 bonds [42] in this order [43]. This fact is supported by theoretical calculations, which show that the product in the 1-2 position is the most stable, followed by the 5-6 isomer [44]. Several reports have indicated that C 60 and C 70 differ in their rates of reactivity.…”