ONIOM Studies of Amidation at Carbon Nanotube Tips: B3LYP for the Expanded Higher Level

In order to study how the choice of model chemistry can affect the results for amidation reaction of carboxylated single-walled carbon nanotubes (SWNTs) with methylamine, we employed ONIOM(B3LYP/STO-3G:UFF) calculations on SWNT models with the higher level expanded to six fused aromatic rings at the nanotube edge. As was observed earlier in the ONIOM(HF/STO3G:UFF) calculations for the same SWNT models, introducing additional carboxylic, hydroxyl, and quinone groups at the higher ONIOM level gives rise to the formation of new hydrogen bonds on the oxidized SWNT models. In many of them, hydrogen atoms move and become shared between neighboring polar groups, sometimes drastically changing the overall geometry of reaction complexes, transition states, and products. The energies for RCs, TSs, and Ps are strongly model-dependent and vary widely. Nevertheless, for any of the models considered, there is some energetic preference for the direct amidation reaction on armchair nanotubes as compared to its zigzag counterpart.