Chemical shielding of doped nitrogen on C20 cage and bowl fullerenes

Abstract

The C₂₀ (cage), C₂₀ (bowl), C₂₀H₁₀ (bowl) fullerene structures and their nitrogen doped derivatives such as C₂₀NH (cage), C₂₀NH (bowl), C₂₀H₁₀N (bowl), C₂₀H₁₀NH (bowl) are fully optimized at the MPW1PW91/6-31G level of theory. The natural atomic charge comparison shows that in C₂₀H₁₀N (bowl), the nitrogen atom with about–0.58 has a more negative charge with respect to other nitrogen doped structures. The nuclear magnetic resonance chemical shielding is evaluated for nitrogen doped structures and the neighbors connected to nitrogen, C₆, and C₇ atoms. The nitrogen atom doped on carbon sites of C₂₀H₁₀N (bowl) has the largest shielding isotropic shifts to the upper field (–203.58 ppm). This means that the electron density around nitrogen in the C₂₀H₁₀N (bowl) structure is higher. Interestingly, there is a significant correlation between the charges and σ_iso values of nitrogen and carbon atoms (C₆ and C₇). Namely, as the charge becomes more negative, σ_iso shifts to the upper field. It is predicted that nitrogen doped C₂₀H₁₀N (bowl) with the maximum electron density adopts this structure for electrophilic reactions.