Nonclassical Fullerene Research Articles

Aromaticity of C 32 fullerene isomers and the 2( N+1) 2 rule

Aromatic character of classical and non-classical fullerene isomers of C 32 was analyzed in terms of Hess–Schaad resonance energy (HSRE), topological resonance energy (TRE), bond resonance energy (BRE) and the 2( N+1) 2 rule of spherical aromaticity. According to the 2( N+1) 2 rule, C 32 fullerene isomers must be highly aromatic with a closed-shell electronic configuration. However, they are predicted to be antiaromatic with negative TREs, negative HSREs and large negative BREs. Two of the isomers have half-filled degenerate HOMOs, which is incompatible with the 2( N+1) 2 rule. Since they all are aromatized by acquiring two more electrons, it is obvious that the neutral C 32 species do not have a maximum degree of aromaticity. Thus, the aromaticity of a fullerene cage is strongly dependent on the connectivity of carbon atoms.

Synthesis of Stable Derivatives of C62: The First Nonclassical Fullerene Incorporating a Four-Membered Ring

A rational synthetic approach to the first four-membered ring-containing derivatives of C(62) is reported. They were synthesized by an inverse electron demand Diels-Alder reaction of 3,6-diaryl-1,2,4,5-tetrazines with C(60) in o-dichlorobenzene, followed by visible light irradiation at reflux. The structure of these nonclassical fullerenes derivatives was determined by X-ray single-crystal diffraction.

Fullerene growth and the role of nonclassical isomers

We report results of a survey of the energetics and stability of classical and 1-heptagon nonclassical fullerene clusters in the range of sizes ${\mathrm{C}}_{30}$ to ${\mathrm{C}}_{70},$ using both total-energy tight-binding and first-principles density functional theory methods. We conclude from this survey that 1-heptagon isomers of high stability exist at every nuclearity, and that these nonclassical isomers play an important part in the growth mechanism of fullerenes.

C62, a Non-Classical Fullerene Incorporating a Four-Membered Ring

C₆₂, a Non-Classical Fullerene Incorporating a Four-Membered Ring